feat: adding cluster size as title for Markers

[kikoso]

Thank you for opening a Pull Request!

---

Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• [ ] Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• [ ] Edit the title of this pull request with a semantic commit prefix (e.g. "fix: "), which is necessary for automated release workflows to decide whether to generate a new release and what type it should be.
• [ ] Will this cause breaking changes to existing Java or Kotlin integrations? If so, ensure the commit has a BREAKING CHANGE footer so when this change is integrated a major version update is triggered. See: https://www.conventionalcommits.org/en/v1.0.0/
• [ ] Ensure the tests and linter pass
• [ ] Code coverage does not decrease (if any source code was changed)
• [ ] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

[googlemaps-bot]

Code Coverage

Overall Project	34.33% -0.09%	:green_apple:
Files changed	0%	:x:

File	Coverage
DefaultClusterRenderer.java	0% -1.04%	:x: