fix: make service ports configurable

[TOGEP]

Summary

Make the MySQL and UI Service ports configurable through values.yaml
Also replace hard-coded ports in the Lake and Grafana endpoints with their existing configured values.
Fixes #372

Changes

• Add mysql.service.port (default: 3306)
• Add ui.service.port (default: 4000)
• Document the new values in HelmSetup.md

The default values remain unchanged, so existing installations are not affected.

[TOGEP]

lake.port was introduced in #144, but this endpoint continued to use the hard-coded port 8080

[TOGEP]

🤔

https://github.com/apache/devlake-helm-chart/actions/runs/32338299965/job/96645343915#step:2:39

  /usr/local/bin/kind: line 1: !DOCTYPE: No such file or directory
  /usr/local/bin/kind: line 2: !--
  /usr/local/bin/kind: line 4: Hello: command not found
  /usr/local/bin/kind: line 7: unexpected EOF while looking for matching `''

[TOGEP]

The mysql-external job failed while downloading the kind binary and appears to be a transient CI issue.
The parallel mysql-builtin job completed successfully

I do not have permission to re-run the failed job. Could a maintainer please re-run it?

[klesh]

LGTM
Thanks for your contribution.