## What changed?
Adds and integrates `yamlfmt` (Go-based, by Google).
Anything not annotated was changed by `yamlfmt`.
## Why?
Consistent YAML formatting. Reduce unrelated diffs caused by formatting
in PRs.
## How did you test it?
- [ ] built
- [ ] run locally and tested manually
- [x] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)
## What changed?
<!-- Describe what has changed in this PR -->
Remove support for Cassandra as visibility store.
Updated integration tests that used Cassandra visibility to use
Elasticsearch.
## Why?
<!-- Tell your future self why have you made these changes -->
Deprecating Cassandra visibility.
## How did you test it?
<!-- How have you verified this change? Tested locally? Added a unit
test? Checked in staging env? -->
Updated tests.
## Potential risks
<!-- Assuming the worst case, what can be broken when deploying this
change to production? -->
No.
## Is hotfix candidate?
<!-- Is this PR a hotfix candidate or does it require a notification to
be sent to the broader community? (Yes/No) -->
No.
