[bitnami/airflow] Add missing LDAP environment variables

[fevisera]

Description of the change

Trying to reproduce #48234 I came across some LDAP environment variables that are being missed.

$ docker-compose -f docker-compose-ldap.yml up -d
$ docker-compose -f docker-compose-ldap.yml logs -f airflow
airflow-airflow-1  | airflow 08:04:48.96 
airflow-airflow-1  | airflow 08:04:48.97 Welcome to the Bitnami airflow container
airflow-airflow-1  | airflow 08:04:48.97 Subscribe to project updates by watching https://github.com/bitnami/containers
airflow-airflow-1  | airflow 08:04:48.97 Submit issues and feature requests at https://github.com/bitnami/containers/issues
airflow-airflow-1  | airflow 08:04:48.97 
airflow-airflow-1  | airflow 08:04:48.98 INFO  ==> Enabling non-root system user with nss_wrapper
airflow-airflow-1  | airflow 08:04:49.00 INFO  ==> ** Starting Airflow setup **
airflow-airflow-1  | airflow 08:04:49.01 INFO  ==> Validating settings in POSTGRESQL_CLIENT_* env vars
airflow-airflow-1  | airflow 08:04:49.05 ERROR ==> Missing AIRFLOW_LDAP_ROLES_MAPPING
airflow-airflow-1  | airflow 08:04:49.05 ERROR ==> Missing AIRFLOW_LDAP_USER_REGISTRATION_ROLE

To prevent the occurrence of missing messages, we should include the following variables: AIRFLOW_LDAP_ROLES_MAPPING and AIRFLOW_LDAP_USER_REGISTRATION_ROLE.

Benefits

Users have a docker-compose-ldap.yml preconfigured with all the necessary environment variables.

Possible drawbacks

N/A

[dgomezleon]

LGTM