Chore: break LDAP manager into smaller pieces to improve unit tests (#26994)

* break LDAP manager into smaller pieces to improve unit tests

* Fix

* Apply suggestions from code review

Co-authored-by: Diego Sampaio <chinello@gmail.com>

* Apply suggestions from code review

Co-authored-by: Pierre Lehnen <55164754+pierre-lehnen-rc@users.noreply.github.com>

* Added few tests

Co-authored-by: Diego Sampaio <chinello@gmail.com>
Co-authored-by: Pierre Lehnen <55164754+pierre-lehnen-rc@users.noreply.github.com>
Co-authored-by: Tasso Evangelista <tasso.evangelista@rocket.chat>