Add Node.js build dep, remove built js/css files (#9114)

- Added Node.js as build dependency and removes build files from git.
- Added version checks for both Go and Node.js.
- Overhauled the js/css make target to only run when needed.
- Merged the `generate` make target into `build` as per suggestion.

Fixes: https://github.com/go-gitea/gitea/issues/6782
Fixes: https://github.com/go-gitea/gitea/issues/9216

.gitignore

@@ -69,6 +69,8 @@ coverage.all
 /modules/indexer/issues/indexers
 routers/repo/authorized_keys
 /yarn.lock
+/public/js
+/public/css
 
 # Snapcraft
 snap/.snapcraft/
@@ -78,4 +80,4 @@ prime/
 *.snap
 *.snap-build
 *_source.tar.bz2
-.DS_Store
+.DS_Store