Support container removal at exit. Fixes #694 (#714)

This patch adds a new command-line flag (`--rm`) to automatically
stop workflow container(s), just prior to exit. The default
behavior is kept, e.g.: the containers continue running at exit.

Fixes: #694
Signed-off-by: Joseph Benden <joe@benden.us>

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

cmd/input.go

@@ -34,6 +34,7 @@ type Input struct {
 	githubInstance        string
 	containerCapAdd       []string
 	containerCapDrop      []string
+	autoRemove            bool
 }
 
 func (i *Input) resolve(path string) string {