Propagate context and ensure git commands run in request context (#17868)

This PR continues the work in #17125 by progressively ensuring that git
commands run within the request context.

This now means that the if there is a git repo already open in the context it will be used instead of reopening it.

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

services/mailer/mail_issue.go

@@ -5,6 +5,7 @@
 package mailer
 
 import (
+	"context"
 	"fmt"
 
 	"code.gitea.io/gitea/models"
@@ -21,6 +22,7 @@ func fallbackMailSubject(issue *models.Issue) string {
 }
 
 type mailCommentContext struct {
+	context.Context
 	Issue      *models.Issue
 	Doer       *user_model.User
 	ActionType models.ActionType