Check volumes (#60)

This PR adds a `ValidVolumes` config. Users can specify the volumes (including bind mounts) that can be mounted to containers by this config.

Options related to volumes:
- [jobs.<job_id>.container.volumes](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idcontainervolumes)
- [jobs.<job_id>.services.<service_id>.volumes](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idservicesservice_idvolumes)

In addition, volumes specified by `options` will also be checked.

Currently, the following default volumes (see a72822b3f8/pkg/runner/run_context.go (L116-L166)) will be added to `ValidVolumes`:
- `act-toolcache`
- `<container-name>` and `<container-name>-env`
- `/var/run/docker.sock` (We need to add a new configuration to control whether the docker daemon can be mounted)

Co-authored-by: Jason Song <i@wolfogre.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/60
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-committed-by: Zettat123 <zettat123@gmail.com>

pkg/runner/runner.go

@@ -68,6 +68,7 @@ type Config struct {
 	PlatformPicker        func(labels []string) string // platform picker, it will take precedence over Platforms if isn't nil
 	JobLoggerLevel        *log.Level                   // the level of job logger
 	Vars                  map[string]string            // the list of variables set at the repository, environment, or organization levels.
+	ValidVolumes          []string                     // only volumes (and bind mounts) in this slice can be mounted on the job container or service containers
 }
 
 // GetToken: Adapt to Gitea