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>

models/repo/repo.go

@@ -485,8 +485,9 @@ func (repo *Repository) CanEnableEditor() bool {
 }
 
 // DescriptionHTML does special handles to description and return HTML string.
-func (repo *Repository) DescriptionHTML() template.HTML {
+func (repo *Repository) DescriptionHTML(ctx context.Context) template.HTML {
 	desc, err := markup.RenderDescriptionHTML(&markup.RenderContext{
+		Ctx:       ctx,
 		URLPrefix: repo.HTMLURL(),
 		Metas:     repo.ComposeMetas(),
 	}, repo.Description)