Config: Support MARIADB_AUTO_UPGRADE and MARIADB_* prefix for environment variables

[lastzero]

When I tested your image for our @photoprism config examples at https://dl.photoprism.app/docker/, I noticed that it does not seem to support the same env variables as the original image (which is not available for ARMv7 though):

https://hub.docker.com/_/mariadb

Adding MARIADB_AUTO_UPGRADE would be very useful as well, so inexperienced users don't need to run migrations manually:

MARIADB_AUTO_UPGRADE: "1"
MARIADB_DATABASE: "photoprism"
MARIADB_USER: "photoprism"
MARIADB_PASSWORD: "insecure"
MARIADB_ROOT_PASSWORD: "insecure"

Unfortunately, we are very busy with our own project, so I don't have time to contribute/send a PR. If anyone has time to implement this, I think it would be very useful for others. Thank you very much!

[dominictayloruk]

I haven't realised that the official MariaDB had changed the MYSQL_* to MARIADB_* variables, i can look into that.

Auto upgrade can be run by mysql_upgrade within the container. This could be done within the scripts after container start.