Simplify the runner docs and fix their outdated facts (#600)

The runner pages had drifted from the runner. They claimed Podman is unsupported, a registration retry limit of 10, a `container.env` proxy override that has no effect, and they used the deprecated `generate-config` command, while the actual instructions were buried under implementation details.

The develop and 5.x pages are rewritten from the current runner sources (`main` is `v5.2.0`). They are shorter and aimed at operators, with a new page covering what jobs get. The reference generator now documents the `config` command, and the quickstart pages in every language use the `gitea-runner` binary name.

Reviewed-on: https://gitea.com/gitea/docs/pulls/600
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

runner-docs_versioned_sidebars/version-5-sidebars.json

@@ -18,6 +18,7 @@
     "registration",
     "configuration",
     "labels",
+    "jobs",
     "cache",
     "proxy",
     {