Make Requests Processes and create process hierarchy. Associate OpenRepository with context. (#17125)

This PR registers requests with the process manager and manages hierarchy within the processes.

Git repos are then associated with a context, (usually the request's context) - with sub commands using this context as their base context.

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

modules/git/repo_tree_nogogit.go

@@ -12,7 +12,7 @@ import (
 )
 
 func (repo *Repository) getTree(id SHA1) (*Tree, error) {
-	wr, rd, cancel := repo.CatFileBatch()
+	wr, rd, cancel := repo.CatFileBatch(repo.Ctx)
 	defer cancel()
 
 	_, _ = wr.Write([]byte(id.String() + "\n"))