fix: hide masked values in log files (#1011)

this commit adds support for the `::add-mask::` command, which was
implemented as a stub before.

it does not cover debug output that appears when you run act in
verbose mode

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>
Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>
Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

pkg/runner/run_context.go

@@ -46,6 +46,11 @@ type RunContext struct {
 	Composite        *model.Action
 	Inputs           map[string]interface{}
 	Parent           *RunContext
+	Masks            []string
+}
+
+func (rc *RunContext) AddMask(mask string) {
+	rc.Masks = append(rc.Masks, mask)
 }
 
 func (rc *RunContext) Clone() *RunContext {