Improve trace logging for pulls and processes (#22633) (#22812)

Backport #22633

Our trace logging is far from perfect and is difficult to follow.

This PR:

* Add trace logging for process manager add and remove.
* Fixes an errant read file for git refs in getMergeCommit
* Brings in the pullrequest `String` and `ColorFormat` methods
introduced in #22568
* Adds a lot more logging in to testPR etc.

Ref #22578

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

modules/log/colors.go

@@ -384,6 +384,13 @@ func (cv *ColoredValue) Format(s fmt.State, c rune) {
 	s.Write(*cv.resetBytes)
 }
 
+// ColorFormatAsString returns the result of the ColorFormat without the color
+func ColorFormatAsString(colorVal ColorFormatted) string {
+	s := new(strings.Builder)
+	_, _ = ColorFprintf(&protectedANSIWriter{w: s, mode: removeColor}, "%-v", colorVal)
+	return s.String()
+}
+
 // SetColorBytes will allow a user to set the colorBytes of a colored value
 func (cv *ColoredValue) SetColorBytes(colorBytes []byte) {
 	cv.colorBytes = &colorBytes