Include LDAP UID attr in default attrs for LDAP lookups

What does this MR do?

Fixes #212465 (closed)

In cases where the configured LDAP uid attribute is non-standard (not uid, samaccountname, userid) the username value in the LDAP auth hash will not contain a value. By including the configured uid attribute in the username default attributes array we ensure that the value will be present in the auth hash.

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Does this MR meet the acceptance criteria?

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