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>

tools/fuzz.go

@@ -9,6 +9,7 @@ package fuzz
 
 import (
 	"bytes"
+	"context"
 	"io"
 
 	"code.gitea.io/gitea/modules/markup"
@@ -25,6 +26,7 @@ import (
 
 var (
 	renderContext = markup.RenderContext{
+		Ctx:       context.Background(),
 		URLPrefix: "https://example.com/go-gitea/gitea",
 		Metas: map[string]string{
 			"user": "go-gitea",