feat: support ldap in pgproto

Summary

• feat: add ldap support to pgproto

The patch adds support of ldap auth method to pgproto. For ldap we request user password in clear text using corresponding protocol message. Afterwards password is passed to tarantool authenticate method which handles ldap based auth.

Important: since password is transferred as clear text it is advised to setup ssl.

• test: refactor ldap machinery, so it is available to other tests too

• test: run ldap test in CI (setup glauth)

Previously we didnt run it because glauth was missing from our image.

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• Close #1241 (closed)
• Cherry-pick to: none
• Docs follow-up: docs#429
• Changelog is updated