Add support for container kernel capabilities (#716)

This patch adds two new command-line flags to specify one or
more kernel capabilities to add or remove from the workflow
containers.

The command-line flag `--container-cap-add` allows for adding
specific capabilities on the workflow containers; where as,

The command-line flag `--container-cap-drop` allows for removing
specific capabilities on the workflow containers.

This was developed to specifically be able to add `SYS_PTRACE`
to a workflow I maintain. It involves using this capability to
monitor a make build, to then build a compilation database.

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

cmd/input.go

@@ -32,6 +32,8 @@ type Input struct {
 	noWorkflowRecurse     bool
 	useGitIgnore          bool
 	githubInstance        string
+	containerCapAdd       []string
+	containerCapDrop      []string
 }
 
 func (i *Input) resolve(path string) string {