Add Open LDAP container

[elaman]

Proposal

There is a module Lightweight Directory Access Protocol (LDAP) which is used by 21k users including me. Also, there is a docker image osixia/openldap with 52M docker pulls including mine.

I propose to include it in this project because it is heavily used by docker users.

Notes

It is quite easy to set up as it is, but for better details, one can read this blog post: Ldap + Identity Server Series ー Part I ー OpenLdap on docker container

[csandanov]

Hi, thanks for the PR however I don't think we're going to merge this, we don't aspire to cover every use case with docker4drupal's default set of images, and I don't think many people need ldap in their local environment