Extended from Osixia/phpldapadmin

  - Adds ca-certificates package
  - Points ldap.conf TLS_CACERT to the ISRG Root X1 CA (allows using let's Encrypt certificates for ldaps) 
  - Rips out the config.php bootstrap from startup
  - Expects an existing config (ie a volume mounted configMap) present at /container/service/phpldapadmin/assets/config/config.php 
  - The read-only config mount will be copied to /var/www/phpldapadmin/config/config.php at startup and chowned to www-data