Add Goroutine stack inspector to admin/monitor (#19207)

Continues on from #19202.

Following the addition of pprof labels we can now more easily understand the relationship between a goroutine and the requests that spawn them. 

This PR takes advantage of the labels and adds a few others, then provides a mechanism for the monitoring page to query the pprof goroutine profile.

The binary profile that results from this profile is immediately piped in to the google library for parsing this and then stack traces are formed for the goroutines.

If the goroutine is within a context or has been created from a goroutine within a process context it will acquire the process description labels for that process. 

The goroutines are mapped with there associate pids and any that do not have an associated pid are placed in a group at the bottom as unbound.

In this way we should be able to more easily examine goroutines that have been stuck.

A manager command `gitea manager processes` is also provided that can export the processes (with or without stacktraces) to the command line.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/process/error.go

@@ -0,0 +1,26 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package process
+
+import "fmt"
+
+// Error is a wrapped error describing the error results of Process Execution
+type Error struct {
+	PID         IDType
+	Description string
+	Err         error
+	CtxErr      error
+	Stdout      string
+	Stderr      string
+}
+
+func (err *Error) Error() string {
+	return fmt.Sprintf("exec(%s:%s) failed: %v(%v) stdout: %s stderr: %s", err.PID, err.Description, err.Err, err.CtxErr, err.Stdout, err.Stderr)
+}
+
+// Unwrap implements the unwrappable implicit interface for go1.13 Unwrap()
+func (err *Error) Unwrap() error {
+	return err.Err
+}