docs: Improve LDAP documentation (#1921)
docs: Improve LDAP documentation (#1921)

* docs(ldap): Make DOVECOT_PASS_FILTER clearer and add a small DOVECOT_AUTH_BIND section

* docs(ldap): Remove superfluous environment variables as of #1989

* docs(ldap): Document defaults for DOVECOT_*_ATTRS/FILTER

* docs(ldap): Add documentation for LDAP with TLS and StartTLS

Co-authored-by: Frederic Werner <cc73abb1270f01c6b5cac77a8bc24ebb0a0e760f@users.noreply.github.com>
Co-authored-by: Brennan Kinney <901e3df23fbf3fa06dbd02d7dc18fa953b9694f7@users.noreply.github.com>
tomav/docker-mailserver,tomav/docker-mailserver,tomav/docker-mailserver