[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/github.com/prometheus/procfs/proc_interrupts.go

@@ -0,0 +1,98 @@
+// Copyright 2022 The Prometheus 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 procfs
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+
+	"github.com/prometheus/procfs/internal/util"
+)
+
+// Interrupt represents a single interrupt line.
+type Interrupt struct {
+	// Info is the type of interrupt.
+	Info string
+	// Devices is the name of the device that is located at that IRQ
+	Devices string
+	// Values is the number of interrupts per CPU.
+	Values []string
+}
+
+// Interrupts models the content of /proc/interrupts. Key is the IRQ number.
+// - https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/s2-proc-interrupts
+// - https://raspberrypi.stackexchange.com/questions/105802/explanation-of-proc-interrupts-output
+type Interrupts map[string]Interrupt
+
+// Interrupts creates a new instance from a given Proc instance.
+func (p Proc) Interrupts() (Interrupts, error) {
+	data, err := util.ReadFileNoStat(p.path("interrupts"))
+	if err != nil {
+		return nil, err
+	}
+	return parseInterrupts(bytes.NewReader(data))
+}
+
+func parseInterrupts(r io.Reader) (Interrupts, error) {
+	var (
+		interrupts = Interrupts{}
+		scanner    = bufio.NewScanner(r)
+	)
+
+	if !scanner.Scan() {
+		return nil, errors.New("interrupts empty")
+	}
+	cpuNum := len(strings.Fields(scanner.Text())) // one header per cpu
+
+	for scanner.Scan() {
+		parts := strings.Fields(scanner.Text())
+		if len(parts) == 0 { // skip empty lines
+			continue
+		}
+		if len(parts) < 2 {
+			return nil, fmt.Errorf("%w: Not enough fields in interrupts (expected 2+ fields but got %d): %s", ErrFileParse, len(parts), parts)
+		}
+		intName := parts[0][:len(parts[0])-1] // remove trailing :
+
+		if len(parts) == 2 {
+			interrupts[intName] = Interrupt{
+				Info:    "",
+				Devices: "",
+				Values: []string{
+					parts[1],
+				},
+			}
+			continue
+		}
+
+		intr := Interrupt{
+			Values: parts[1 : cpuNum+1],
+		}
+
+		if _, err := strconv.Atoi(intName); err == nil { // numeral interrupt
+			intr.Info = parts[cpuNum+1]
+			intr.Devices = strings.Join(parts[cpuNum+2:], " ")
+		} else {
+			intr.Info = strings.Join(parts[cpuNum+1:], " ")
+		}
+		interrupts[intName] = intr
+	}
+
+	return interrupts, scanner.Err()
+}