[chore] Add Go runtime and host metrics (#4137)

Daenney is a dummy and forgot to add these when he revamped the OTEL stuff.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4137
Co-authored-by: Daenney <daenney@noreply.codeberg.org>
Co-committed-by: Daenney <daenney@noreply.codeberg.org>

vendor/go.opentelemetry.io/contrib/instrumentation/runtime/internal/x/README.md

@@ -0,0 +1,38 @@
+# Feature Gates
+
+The runtime package contains a feature gate used to ease the migration
+from the [previous runtime metrics conventions] to the new [OpenTelemetry Go
+Runtime conventions].
+
+Note that the new runtime metrics conventions are still experimental, and may
+change in backwards incompatible ways as feedback is applied.
+
+## Features
+
+- [Include Deprecated Metrics](#include-deprecated-metrics)
+
+### Include Deprecated Metrics
+
+Once new experimental runtime metrics are added, they will be produced
+**in addition to** the existing runtime metrics. Users that migrate right away
+can disable the old runtime metrics:
+
+```console
+export OTEL_GO_X_DEPRECATED_RUNTIME_METRICS=false
+```
+
+In a later release, the deprecated runtime metrics will stop being produced by
+default. To temporarily re-enable the deprecated metrics:
+
+```console
+export OTEL_GO_X_DEPRECATED_RUNTIME_METRICS=true
+```
+
+After two additional releases, the deprecated runtime metrics will be removed,
+and setting the environment variable will no longer have any effect.
+
+The value set must be the case-insensitive string of `"true"` to enable the
+feature, and `"false"` to disable the feature. All other values are ignored.
+
+[previous runtime metrics conventions]: https://pkg.go.dev/go.opentelemetry.io/contrib/instrumentation/runtime@v0.52.0
+[OpenTelemetry Go Runtime conventions]: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/runtime/go-metrics.md

vendor/go.opentelemetry.io/contrib/instrumentation/runtime/internal/x/x.go

@@ -0,0 +1,53 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package x contains support for OTel runtime instrumentation experimental features.
+//
+// This package should only be used for features defined in the specification.
+// It should not be used for experiments or new project ideas.
+package x // import "go.opentelemetry.io/contrib/instrumentation/runtime/internal/x"
+
+import (
+	"os"
+	"strings"
+)
+
+// DeprecatedRuntimeMetrics is an experimental feature flag that defines if the deprecated
+// runtime metrics should be produced. During development of the new
+// conventions, it is enabled by default.
+//
+// To disable this feature set the OTEL_GO_X_DEPRECATED_RUNTIME_METRICS environment variable
+// to the case-insensitive string value of "false" (i.e. "False" and "FALSE"
+// will also enable this).
+var DeprecatedRuntimeMetrics = newFeature("DEPRECATED_RUNTIME_METRICS", true)
+
+// BoolFeature is an experimental feature control flag. It provides a uniform way
+// to interact with these feature flags and parse their values.
+type BoolFeature struct {
+	key        string
+	defaultVal bool
+}
+
+func newFeature(suffix string, defaultVal bool) BoolFeature {
+	const envKeyRoot = "OTEL_GO_X_"
+	return BoolFeature{
+		key:        envKeyRoot + suffix,
+		defaultVal: defaultVal,
+	}
+}
+
+// Key returns the environment variable key that needs to be set to enable the
+// feature.
+func (f BoolFeature) Key() string { return f.key }
+
+// Enabled returns if the feature is enabled.
+func (f BoolFeature) Enabled() bool {
+	v := os.Getenv(f.key)
+	if strings.ToLower(v) == "false" {
+		return false
+	}
+	if strings.ToLower(v) == "true" {
+		return true
+	}
+	return f.defaultVal
+}