[Mail] Merge MTA and MDA, add doc, build via Compose and secrets

deprecated/pica-mail-copy-certs/Dockerfile

deprecated/pica-mail-copy-certs/README.md

deprecated/pica-mail-copy-certs/update-certs-pica-mail.sh

docker-compose/README.md

docker-compose/mail.yml

pica-grafana-prom/README.md

pica-mail/.env

pica-mail/README.md

pica-mail/docker-compose.yml

pica-mail/pica-mail-mda/Dockerfile

pica-mail/pica-mail-mda/README.md

pica-mail/pica-mail-mda/entrypoint.sh

pica-mail/pica-mail-mda/fichiers_de_configuration.sh

pica-mail/pica-mail-mta/Dockerfile

pica-mail/pica-mail-mta/README.md

pica-mail/pica-mail-mta/config.sh

pica-mail/pica-mail-mta/entrypoint.sh

pica-mail/pica-mail-mta/local_mailbox_ldap_sasl/Dockerfile

pica-mail/pica-mail-mta/local_mailbox_ldap_sasl/README.md

...mail/pica-mail-mta/local_mailbox_ldap_sasl/entrypoint2.sh