docs: document automatic MySQL port detection

[slayerjain]

What has changed?

Documents automatic MySQL port detection, shipped in keploy/keploy#4389.

Keploy used to route MySQL to its parser purely by destination port — 3306 and 4000 by default, plus whatever mysqlPorts listed. MySQL on any other port (a second instance on 3307, ProxySQL on 6033, MaxScale on 4006, StarRocks on 9030, a Cloud SQL Auth Proxy) could not complete its handshake, and the application failed to connect.

Two documentation gaps made that worse than it needed to be:

1. mysqlPorts was never documented anywhere. It existed only in the source. A user hitting the problem had no discoverable fix.
2. Nothing described the symptom. The error users actually search for is Lost connection to server at 'handshake: reading initial communication packet', and it appeared nowhere in the docs.

Changes

running-keploy/configuration-file.md

• Adds mysqlPorts and disableMysqlAutoDetect to the sample config block, matching what keploy config --generate now emits.
• Adds a MySQL port detection section explaining how detection works in each mode — Keploy reads the server's handshake during Record, and recovers the port from recorded Mocks during Test (no database is running then, so the port cannot come from anywhere else).
• Documents when either field is worth setting, and warns that disabling detection means listing every MySQL port your application uses.

keploy-explained/common-errors.md

• Adds troubleshooting entry 12 for the stuck-handshake symptom, with the exact error string, both causes, and the fix. Cross-links to the section above.

This is a documentation-only change — no behaviour is described that isn't already merged or in review upstream.

This PR Resolves #(issue) — NA

Type of change

• Documentation update (if none of the other choices apply).

How Has This Been Tested?

Both commands run clean locally:

• npm run build → exits 0, [SUCCESS] Generated static files in "build", 205 documents processed, no broken-link warnings (the new relative link from the troubleshooting entry into the config reference anchor resolves).
• npx prettier@2.8.8 --check on both files → All matched files use Prettier code style!
• vale 3.0.3 --config=.vale.ini on both files → the only remaining alerts are on pre-existing lines I did not touch (matchType, hardcoding, xml, json, traceroute); CI runs with filter_mode: diff_context, so none of them apply to this diff. No alerts on any added line.

No screenshots attached — the change is prose and a config snippet with no new visual elements. Happy to add one of the rendered MySQL port detection section if you'd like it in the PR.

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.