Fix attest with --key (#2551)

Fix passing "--key" to the attest command. Additionally, pull in an update to
the clio CLI library to permit unit testing that flags and env vars are parsed
to the correct field on command options structs. This testing strategy was
needed here because testing attestation in an end to end test requires a
prohibitive amount of setup.

---------

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>
Signed-off-by: Will Murphy <will.murphy@anchore.com>
Co-authored-by: Alex Goodman <wagoodman@users.noreply.github.com>

test/cli/scan_cmd_test.go

@@ -191,6 +191,7 @@ func TestPackagesCmdFlags(t *testing.T) {
 			},
 		},
 		{
+			// TODO: this could be a unit test
 			name: "responds-to-package-cataloger-search-options",
 			args: []string{"--help"},
 			env: map[string]string{