Provide diff and patch API endpoints (#11751)

* Provide diff and patch API endpoints

The diff and patch endpoints on the main routes are not accessible by token
therefore we provide new API based endpoints for these

Fix #10923

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

* placate swagger

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

* Make the response an actual string

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

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

modules/context/api.go

@@ -65,6 +65,10 @@ type APINotFound struct{}
 // swagger:response redirect
 type APIRedirect struct{}
 
+//APIString is a string response
+// swagger:response string
+type APIString string
+
 // Error responds with an error message to client with given obj as the message.
 // If status is 500, also it prints error to log.
 func (ctx *APIContext) Error(status int, title string, obj interface{}) {