[Bug]: reduce ldap_dn field to 4000 bytes

[blizzz]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Oracle, by default, limits varchar2 types to 4000 bytes (cf. #31679). In https://github.com/nextcloud/server/blob/v22.2.5/apps/user_ldap/lib/Migration/Version1130Date20211102154716.php#L118-L122 we increase it from 255 to 4096 bytes, which may lead into invalid data conversion type issues (it seems).

Steps to reproduce

1. have Oracle with MAX_STRING_SIZE set to Standard
2. upgrade from e.g. 22.2.3 to current stable22

Expected behavior

Smooth upgrade

Installation method

No response

Operating system

No response

PHP engine version

No response

Web server

No response

Database engine version

Oracle

Is this bug present after an update or on a fresh install?

Updated from a minor version (ex. 22.2.3 to 22.2.4)

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

not relevant

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

[blizzz]

@come-nc would we expact major issues here?