Add LDAP support

[schnerring]

LDAP support was added to Etebase a couple of weeks ago. It supports easy config, so integrating it into this Docker image should be straightforward:

https://github.com/etesync/server/blob/master/etebase-server.ini.example#L25-L35

;[ldap]
;server = <The URL to your LDAP server>
;search_base = <Your search base>
;filter = <Your LDAP filter query. '%%s' will be substituted for the username>
; In case a cache TTL of 1 hour is too short for you, set `cache_ttl` to the preferred
; amount of hours a cache entry should be viewed as valid:
;cache_ttl = 5
;bind_dn = <Your LDAP "user" to bind as. Must be a bind user>
; Either specify the password directly, or provide a password file
;bind_pw = <The password to authenticate as your bind user>
;bind_pw_file = /path/to/the/file.txt

[victor-rds]

I've already added the necessary dependencies on the last image, libldap and libsasl, but you need to edit the ini file manually.

Updating the script is on my TODO list.