Stop packaging node_modules in release tarballs (#15273)

- Don't package node_modules in tarballs, they are not cross-platform
  anymore and npm cache should not be messed with directly. Instead,
  require an internet connection to rebuild the UI, which is not necessary
  in the general use case because prebuilt UI files are shipped in the
  public directory.
- Simplify the fomantic build and make the target phony. We don't need
  anything more for something that is rarely ran.
- Use regular tar again to build tarballs and add variable for excludes
- Disable annoying npm update notifications

Fixes: https://github.com/go-gitea/gitea/pull/14578
Fixes: https://github.com/go-gitea/gitea/pull/15256
Fixes: https://github.com/go-gitea/gitea/pull/15262

Co-authored-by: 6543 <6543@obermui.de>

README.md

@@ -77,13 +77,11 @@ or if sqlite support is required:
 The `build` target is split into two sub-targets:
 
 - `make backend` which requires [Go 1.13](https://golang.org/dl/) or greater.
-- `make frontend` which requires [Node.js 12.17](https://nodejs.org/en/download/) or greater.
+- `make frontend` which requires [Node.js 12.17](https://nodejs.org/en/download/) or greater and Internet connectivity to download npm dependencies.
 
-If pre-built frontend files are present it is possible to only build the backend:
+When building from the official source tarballs which include pre-built frontend files, the `frontend` target will not be triggered, making it possible to build without Node.js and Internet connectivity.
 
-    TAGS="bindata" make backend
-
-Parallelism is not supported for these targets, so please don't include `-j <num>`.
+Parallelism (`make -j <num>`) is not supported.
 
 More info: https://docs.gitea.io/en-us/install-from-source/