[GITEA] Add support for shields.io-based badges

Adds a new `/{username}/{repo}/badges` family of routes, which redirect
to various shields.io badges. The goal is to not reimplement badge
generation, and delegate it to shields.io (or a similar service), which
are already used by many. This way, we get all the goodies that come
with it: different styles, colors, logos, you name it.

So these routes are just thin wrappers around shields.io that make it
easier to display the information we want. The URL is configurable via
`app.ini`, and is templatable, allowing to use alternative badge
generator services with slightly different URL patterns.

Additionally, for compatibility with GitHub, there's an
`/{username}/{repo}/actions/workflows/{workflow_file}/badge.svg` route
that works much the same way as on GitHub. Change the hostname in the
URL, and done.

Fixes gitea#5633, gitea#23688, and also fixes #126.

Work sponsored by Codeberg e.V.

Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
(cherry picked from commit fcd0f61212)
(cherry picked from commit 20d14f7844)
(cherry picked from commit 4359741431)

modules/setting/setting.go

@@ -147,6 +147,7 @@ func loadCommonSettingsFrom(cfg ConfigProvider) error {
 	loadUIFrom(cfg)
 	loadAdminFrom(cfg)
 	loadAPIFrom(cfg)
+	loadBadgesFrom(cfg)
 	loadMetricsFrom(cfg)
 	loadCamoFrom(cfg)
 	loadI18nFrom(cfg)