[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

vendor/go.opentelemetry.io/otel/exporters/prometheus/config.go

@@ -0,0 +1,153 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package prometheus // import "go.opentelemetry.io/otel/exporters/prometheus"
+
+import (
+	"strings"
+
+	"github.com/prometheus/client_golang/prometheus"
+
+	"go.opentelemetry.io/otel/sdk/metric"
+)
+
+// config contains options for the exporter.
+type config struct {
+	registerer             prometheus.Registerer
+	disableTargetInfo      bool
+	withoutUnits           bool
+	withoutCounterSuffixes bool
+	readerOpts             []metric.ManualReaderOption
+	disableScopeInfo       bool
+	namespace              string
+}
+
+// newConfig creates a validated config configured with options.
+func newConfig(opts ...Option) config {
+	cfg := config{}
+	for _, opt := range opts {
+		cfg = opt.apply(cfg)
+	}
+
+	if cfg.registerer == nil {
+		cfg.registerer = prometheus.DefaultRegisterer
+	}
+
+	return cfg
+}
+
+// Option sets exporter option values.
+type Option interface {
+	apply(config) config
+}
+
+type optionFunc func(config) config
+
+func (fn optionFunc) apply(cfg config) config {
+	return fn(cfg)
+}
+
+// WithRegisterer configures which prometheus Registerer the Exporter will
+// register with.  If no registerer is used the prometheus DefaultRegisterer is
+// used.
+func WithRegisterer(reg prometheus.Registerer) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.registerer = reg
+		return cfg
+	})
+}
+
+// WithAggregationSelector configure the Aggregation Selector the exporter will
+// use. If no AggregationSelector is provided the DefaultAggregationSelector is
+// used.
+func WithAggregationSelector(agg metric.AggregationSelector) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.readerOpts = append(cfg.readerOpts, metric.WithAggregationSelector(agg))
+		return cfg
+	})
+}
+
+// WithProducer configure the metric Producer the exporter will use as a source
+// of external metric data.
+func WithProducer(producer metric.Producer) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.readerOpts = append(cfg.readerOpts, metric.WithProducer(producer))
+		return cfg
+	})
+}
+
+// WithoutTargetInfo configures the Exporter to not export the resource target_info metric.
+// If not specified, the Exporter will create a target_info metric containing
+// the metrics' resource.Resource attributes.
+func WithoutTargetInfo() Option {
+	return optionFunc(func(cfg config) config {
+		cfg.disableTargetInfo = true
+		return cfg
+	})
+}
+
+// WithoutUnits disables exporter's addition of unit suffixes to metric names,
+// and will also prevent unit comments from being added in OpenMetrics once
+// unit comments are supported.
+//
+// By default, metric names include a unit suffix to follow Prometheus naming
+// conventions. For example, the counter metric request.duration, with unit
+// milliseconds would become request_duration_milliseconds_total.
+// With this option set, the name would instead be request_duration_total.
+func WithoutUnits() Option {
+	return optionFunc(func(cfg config) config {
+		cfg.withoutUnits = true
+		return cfg
+	})
+}
+
+// WithoutCounterSuffixes disables exporter's addition _total suffixes on counters.
+//
+// By default, metric names include a _total suffix to follow Prometheus naming
+// conventions. For example, the counter metric happy.people would become
+// happy_people_total. With this option set, the name would instead be
+// happy_people.
+func WithoutCounterSuffixes() Option {
+	return optionFunc(func(cfg config) config {
+		cfg.withoutCounterSuffixes = true
+		return cfg
+	})
+}
+
+// WithoutScopeInfo configures the Exporter to not export the otel_scope_info metric.
+// If not specified, the Exporter will create a otel_scope_info metric containing
+// the metrics' Instrumentation Scope, and also add labels about Instrumentation Scope to all metric points.
+func WithoutScopeInfo() Option {
+	return optionFunc(func(cfg config) config {
+		cfg.disableScopeInfo = true
+		return cfg
+	})
+}
+
+// WithNamespace configures the Exporter to prefix metric with the given namespace.
+// Metadata metrics such as target_info and otel_scope_info are not prefixed since these
+// have special behavior based on their name.
+func WithNamespace(ns string) Option {
+	return optionFunc(func(cfg config) config {
+		ns = sanitizeName(ns)
+		if !strings.HasSuffix(ns, "_") {
+			// namespace and metric names should be separated with an underscore,
+			// adds a trailing underscore if there is not one already.
+			ns = ns + "_"
+		}
+
+		cfg.namespace = ns
+		return cfg
+	})
+}