fix: Make Vue's ldapGroupMemberAssocAttr label map LcValue-compatible

[j-frei]

Summary

The user_ldap plugin features the field ldapGroupMemberAssocAttr and its values are converted into lowercase when set. In the UI, the field loads the labels using the groupMemberAssociation constant, which used to be case-sensitive.
It failed for all entries other than 'member' because these fields had upper letters in it; resulting in the settings panel to display the GUI field as empty.
This is fixed here. (Tested on v33.0.2)

It could be partially related to #60342, but just viewing the field before this PR did not change the ldap settings in my tests.

[joshtrichards]

Makes sense. As an aside, LDAP configuration frontend could really use test coverage! A future follow-up PR idea for someone.

[joshtrichards]

/backport to stable35

[joshtrichards]

/backport to stable34

[joshtrichards]

/backport to stable33

[joshtrichards]

@j-frei DCO check needs to be remedied https://github.com/nextcloud/server/pull/63672/checks?check_run_id=98282405379

[j-frei]

@joshtrichards Thanks! DCO should be fixed now.

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