Simplify the runner docs and fix their outdated facts (#600)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

docs/usage/actions/quickstart.md

@@ -40,7 +40,7 @@ However, it is recommended to use Docker to run the jobs, because it is more sec
 Before running a runner, you should first register it to your Gitea instance using the following command:
 
 ```bash
-./runner register --no-interactive --instance <instance> --token <token>
+gitea-runner register --no-interactive --instance <instance> --token <token>
 ```
 
 There are two arguments required, `instance` and `token`.
@@ -69,7 +69,7 @@ If this file is missing or corrupted, you can simply remove it and register agai
 Finally, it's time to start the runner:
 
 ```bash
-./runner daemon
+gitea-runner daemon
 ```
 
 And you can see the new runner in the management page: