fix: Correct MySQL deployment guide pool params, SSL modes, and metric name

[claudespice]

Summary

• Connection pool parameter names were wrong: connection_pool_min_idle/connection_pool_size → mysql_pool_min/mysql_pool_max (defined as ParameterSpec::component("pool_min") and component("pool_max") in connector-mysql)
• verify_ca SSL mode was documented but is not implemented — the connector only supports disabled, preferred, and required
• Metric name was wrong: discarded_excess_idle_connection → discarded_superfluous_connection

Changes

• Fixed pool parameter names and updated all references throughout the deployment guide
• Removed verify_ca from the SSL mode table and all references in troubleshooting/limitations
• Corrected the metric name in the metrics table

Reference

Verified against spiceai/spiceai at trunk:

• connector-mysql/src/lib.rs:92-95 (pool params)
• catalogconnector/mysql.rs:172 (SSL mode validation)
• connector-mysql/src/lib.rs:303 (metric name)

[github-actions]

✅ Pull with Spice Passed

Passing checks:

• ✅ Title meets minimum length requirement (10 characters)
• ✅ Has at least one of the required labels: area/blog, area/docs, area/cookbook, dependencies
• ✅ No banned labels detected
• ✅ Has at least one assignee: lukekim

[github-actions]

🚀 deployed to https://657d05cc.spiceai-org-website.pages.dev

[github-actions]

🚀 deployed to https://e7fec991.spiceai-org-website.pages.dev