Enable Istio for MM Operator

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/tags/1.15.0-bb.0

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/merge_requests/22

Couple of BB changes:

• Add values passdown for monitoring/istio/openshift
• Move istio dependency "higher" up (to operator instead of instance)
• Enable injection on the ns
• Bump to latest tag
  • Operator 1.15.0
  • New networkpolicies for the sidecars to work

Closes https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/issues/8