docs: update contributing guide to rebase of origin/master not local master branch

Updating the squash command to reference origin/master instead of the local master branch in the event a local environment's master branch is not up to date.

See merge request platform-one/big-bang/umbrella!150

ci: only run infra jobs on merges to master

See merge request platform-one/big-bang/umbrella!194

Adding default values to grafana.ini templating.

Update tag in values.yaml