Allow to override location of action cache dir (#65)

Adds an explicit config option to specify the directory
below which action contents will be cached. If left empty
the previous location at `$XDG_CACHE_HOME/act` or
`$HOME/.cache/act` will be used respectively.

Required to resolve gitea/act_runner#235

Co-authored-by: Marius Zwicker <marius@mlba-team.de>
Reviewed-on: https://gitea.com/gitea/act/pulls/65
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: Marius Zwicker <emzeat@noreply.gitea.com>
Co-committed-by: Marius Zwicker <emzeat@noreply.gitea.com>

cmd/input.go

@@ -54,6 +54,7 @@ type Input struct {
 	replaceGheActionWithGithubCom      []string
 	replaceGheActionTokenWithGithubCom string
 	matrix                             []string
+	actionCachePath                    string
 }
 
 func (i *Input) resolve(path string) string {