core (memory/sqla_mapping): fix some technical debt: a first Alembic revision file is joined to migrate existing databases to new mapping. This patch: - set `nullable=False` in various places - drop legacy `message_types` table, and use `Enum` instead - use naming convention, and get rid of anonymous constraint (this is the main reason why the revision file is so long)

[DEFAULT]
xmpp_domain = server1.test
email_server = libervia-backend.test
email_port = 8025
email_admins_list = admin@server1.test

[component file_sharing]
tls_certificate = /usr/share/libervia/certificates/server1.test.pem
tls_private_key = /usr/share/libervia/certificates/server1.test-key.pem
http_upload_public_facing_url = https://libervia-backend.test:8888