[melroy89]

Remove obsolete database configuration options and update the PHP connection guidance.

• Retain innodb_buffer_pool_instances as a commented-out option with an inline explanation: it is MySQL-only and was removed in MariaDB 10.6. MySQL 8.4 already defaults to one instance for this example's 128M buffer pool.
• Remove the obsolete innodb_large_prefix and innodb_file_format options.
• Remove MySQL-incompatible query-cache options from the shared example.
• Replace the removed PHP mysql.* extension settings with PDO_MYSQL socket guidance. Include a brief Ubuntu PHP 8.5-FPM example using a separate 99-nextcloud.ini override file, the reload command, and separate CLI configuration guidance. Only override an incorrect default socket path.
• Clarify that some configuration options and include paths depend on the database engine and installation, and correct the MariaDB manual link label.

The repeated obsolete options in config_sample_php_parameters.rst need a separate upstream fix in Nextcloud Server's config.sample.php, since that documentation is generated.

Once merged, please also merge the other PR (in the other repo): nextcloud/server#66121

AI assistance: OpenAI Codex (GPT-6) assisted with the review, documentation changes, local validation, and PR update.

☑️ Resolves

Fix #4758

🖼️ Screenshots

Before:

After (database configuration with the inline MySQL-only comment):

After (compatibility note, PDO socket override, and PHP-FPM/CLI configuration guidance):

✅ Checklist

• I have built the documentation locally and reviewed the output
• Screenshots are included for visual changes
• I have not moved or renamed pages (or added a redirect if I did)
• I have run codespell or similar and addressed any spelling issues

Validation: make -C admin_manual html passed with warnings treated as errors; sphinx-lint, codespell, and git diff --check passed. The rendered page was reviewed in Chrome. Database startup compatibility was not tested.