[openstack-helm] Stepping down as core reviewer

Hey everyone, I hope you're all staying safe and well. I switched jobs a few months back that took me in a different direction from my previous employer, and as a result I've not had the time to remain involved with the OpenStack community (especially as my day job no longer involves working with OpenStack). I think it's best that I step down from the openstack-helm core reviewer team, as I can't realistically make the time to do my due diligence in providing thorough, useful code reviews. I greatly appreciate the opportunities that working with the OpenStack community at large has provided me over the past 5 years. Cheers, srwilkers