Add danielhelfand as OWNER 🐱

Daniel is one of the most active contributor of `tektoncd/cli`,
contributing some new features as well as fixing bugs and doing
refactorings.

He is also quit actively reviewing PR (see
https://tekton.devstats.cd.foundation/d/46/pr-reviews-by-contributor?orgId=1&var-period=d&var-repo_name=tektoncd%2Fcli&var-reviewers=%22danielhelfand%22).

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

Author: vdemeester

OWNERS

@@ -4,4 +4,5 @@ approvers:
 - vdemeester
 - sthaha
 - hrishin
-- chmouel
+- chmouel
+- danielhelfand