armbian-next: GHA & rootfs adventures, pt 1

- rootfs: create readonly global `rootfs_cache_id` (type+hash+date/version)
- add "oras-upload" CLI command (dumb, no retries, single target/single source)
- docker: mount-bind for & re-pass envs `GITHUB_OUTPUT` and `GITHUB_STEP_SUMMARY` down to Docker
- introduce `github-actions.sh::github_actions_add_output()`
- during logs cleanup, dump the Markdown log into GITHUB_STEP_SUMMARY if it is available

lib/functions/cli/cli-requirements.sh

@@ -23,5 +23,7 @@ function cli_requirements_run() {
 
 	LOG_SECTION="install_host_dependencies" do_with_logging install_host_dependencies "for requirements command"
 
+	# @TODO: get stuff like shellcheck, shfmt, and ORAS in here. Deploy them somewhere not-in-./cache, so it's baked into Docker image.
+
 	display_alert "Done with" "@host dependencies" "cachehit"
 }