[Enhancement]: Add support for retrieving PublicKeys attribute to LDAP module

[mattboyd-aws]

Is your idea related to a problem? Please describe.
I store public keys in LDAP/AD attributes and want to retrieve and use those when authenticating users in AD/LDAP instead of manually synchronizing them in the DynamoDB user records.

Describe the solution you'd like
Like the other retrievable LDAP attributes, add support for mapping and retrieving an LDAP attribute for PublicKeys .

P.S. Please do not attach files as it's considered a security risk. Add code snippets directly in the message body as much as possible.