Allow to override location of action cache dir (#1863)

Adds an option to specify the directory below which actions
and host workspaces will be stored. If left empty the previous
location at $XDG_CACHE_HOME/act or $HOME/.cache/act will be used
respectively.

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/runner.go

@@ -22,6 +22,7 @@ type Runner interface {
 type Config struct {
 	Actor                              string                     // the user that triggered the event
 	Workdir                            string                     // path to working directory
+	ActionCacheDir                     string                     // path used for caching action contents
 	BindWorkdir                        bool                       // bind the workdir to the job container
 	EventName                          string                     // name of event to run
 	EventPath                          string                     // path to JSON file to use for event.json in containers