fix: Minor fixes (#1075)

A batch of small, self-contained fixes and docs/example additions.

Fixes #625 - align the example config's `force_pull` with the actual default (`false`)
Fixes #804 - return an error instead of discarding `os.UserHomeDir()` when defaulting `cache.dir`/`host.workdir_parent`
Fixes #571 - send a `gitea-runner/<version>` User-Agent on API requests
Fixes #650 - detect an `Unauthenticated` fetch response and exit the daemon with an error instead of retrying forever
Fixes #766 - add `exec --eventpath` to supply a JSON event payload file
Fixes #256 - add a `bug-report` subcommand that prints version/Go/OS-arch/CPU info
Fixes #617 - add `runner.set_act_env` (default `true`) to optionally omit the `ACT=true` env var
Fixes #635 - record a failure result (and guard a nil reusable-workflow caller) when the job `if`-expression fails to evaluate
Fixes #1005 - remove README docs for config env-var overrides that were already removed from the code
Fixes #448 - clarify in `exec --job` help that `--workflows` may be needed to disambiguate
Fixes #209 - note that `host`-labelled runners still need Docker for `docker://` actions and service containers
Fixes #757 - add a systemd service example with automatic restart
Fixes #474 - add a Kubernetes StatefulSet example that persists the `.runner` registration across reschedules
Fixes #776 - build the basic (non-dind) docker image for `linux/riscv64`
Fixes #628 - build the basic (non-dind) docker image for `linux/s390x`Reviewed-on: https://gitea.com/gitea/runner/pulls/1075
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>

examples/systemd/gitea-runner.service

@@ -0,0 +1,30 @@
+[Unit]
+Description=Gitea Actions runner
+Documentation=https://gitea.com/gitea/runner
+After=network-online.target
+Wants=network-online.target
+# Uncomment when jobs use the local Docker daemon:
+# After=docker.service
+# Requires=docker.service
+
+[Service]
+Type=simple
+# Adjust the binary path, config path and working directory to your setup.
+# The working directory is where the .runner registration file is read from
+# unless runner.file is set to an absolute path in the config.
+ExecStart=/usr/local/bin/gitea-runner daemon --config /etc/gitea-runner/config.yaml
+WorkingDirectory=/var/lib/gitea-runner
+User=gitea-runner
+Group=gitea-runner
+
+# Restart automatically so the runner survives transient failures, e.g. the
+# Gitea instance being temporarily unreachable at startup.
+Restart=on-failure
+RestartSec=5s
+
+# Allow running jobs to finish before the runner is stopped. Keep this in sync
+# with runner.shutdown_timeout in the config.
+TimeoutStopSec=3h
+
+[Install]
+WantedBy=multi-user.target