refactor: markup render (#38864)

1. add missing CSP header to api & web render endpoints.
2. make jupyter render skip post-processors, nothing to process
3. make ShortLinkProcessor correctly validate URL schemes and respect
the CustomURLSchemes setting

modules/markup/main_test.go

@@ -14,7 +14,6 @@ import (
 func TestMain(m *testing.M) {
 	setting.IsInTesting = true
 	markup.RenderBehaviorForTesting.DisableAdditionalAttributes = true
-	setting.Markdown.FileNamePatterns = []string{"*.md"}
 	markup.RefreshFileNamePatterns()
 	os.Exit(m.Run())
 }