#12897 - add mastodon provider (#13293)

* added mastodon provider to oauth code

* changed go.mod and vendor/modules.txt to add updated goth

* vendored mastodon and new goth

* committing result of go mod tidy && go mod vendor

* added pic and mastodon to oauth models

* handled instance url

* applied lafriks suggestion

* Update web_src/js/index.js

Co-authored-by: techknowlogick <matti@mdranta.net>

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

templates/admin/auth/source/oauth.tmpl

@@ -55,4 +55,4 @@
 			<input id="{{$key}}_email_url" value="{{$value.EmailURL}}" type="hidden" />
 		{{end}}
 	{{end}}
-</div>
+</div>