fix(files_external): Handling in FTP UI for custom ports

[joshtrichards]

• Resolves: Setting custom port from GUI broken for FTP and SFTP #32773
• Resolves: External Storage with "other port" usage NEED TO PUT THAT IN DOCUMENT documentation#941

Summary

Docs say we support this, but it is broken in the Web UI. We already handle the port parameter so let's use it properly.

server/apps/files_external/lib/Lib/Storage/FTP.php

Line 47 in 11822de

$this->port = $params['port'] ?? 21;

TODO

• Follow-up PR(s) pending any other backends with similar situations (i.e. SFTP)
• Update doc sections for each backend

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[joshtrichards]

/backport to stable30

[joshtrichards]

/backport to stable29