[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/thread.go

@@ -0,0 +1,80 @@
+// 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 (
+	"fmt"
+	"os"
+	"strconv"
+
+	fsi "github.com/prometheus/procfs/internal/fs"
+)
+
+// Provide access to /proc/PID/task/TID files, for thread specific values. Since
+// such files have the same structure as /proc/PID/ ones, the data structures
+// and the parsers for the latter may be reused.
+
+// AllThreads returns a list of all currently available threads under /proc/PID.
+func AllThreads(pid int) (Procs, error) {
+	fs, err := NewFS(DefaultMountPoint)
+	if err != nil {
+		return Procs{}, err
+	}
+	return fs.AllThreads(pid)
+}
+
+// AllThreads returns a list of all currently available threads for PID.
+func (fs FS) AllThreads(pid int) (Procs, error) {
+	taskPath := fs.proc.Path(strconv.Itoa(pid), "task")
+	d, err := os.Open(taskPath)
+	if err != nil {
+		return Procs{}, err
+	}
+	defer d.Close()
+
+	names, err := d.Readdirnames(-1)
+	if err != nil {
+		return Procs{}, fmt.Errorf("%s: could not read %q: %w", ErrFileRead, d.Name(), err)
+	}
+
+	t := Procs{}
+	for _, n := range names {
+		tid, err := strconv.ParseInt(n, 10, 64)
+		if err != nil {
+			continue
+		}
+
+		t = append(t, Proc{PID: int(tid), fs: FS{fsi.FS(taskPath), fs.isReal}})
+	}
+
+	return t, nil
+}
+
+// Thread returns a process for a given PID, TID.
+func (fs FS) Thread(pid, tid int) (Proc, error) {
+	taskPath := fs.proc.Path(strconv.Itoa(pid), "task")
+	if _, err := os.Stat(taskPath); err != nil {
+		return Proc{}, err
+	}
+	return Proc{PID: tid, fs: FS{fsi.FS(taskPath), fs.isReal}}, nil
+}
+
+// Thread returns a process for a given TID of Proc.
+func (proc Proc) Thread(tid int) (Proc, error) {
+	tfs := FS{fsi.FS(proc.path("task")), proc.fs.isReal}
+	if _, err := os.Stat(tfs.proc.Path(strconv.Itoa(tid))); err != nil {
+		return Proc{}, err
+	}
+	return Proc{PID: tid, fs: tfs}, nil
+}