CI: Check for daily mariadb updates

[jbergstroem]

Create a timed ci job that checks alpine repos for available versions. This could also open an issue or even a PR should a new version be found.

[jbergstroem]

Some info I've collected:

• This is how the script would run periodically: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#onschedule

• One approach to collecting alpine version can be either apk version if mariadb is installed in said environment; apk info if uninstalled - both would have to be parsed though.

• Another approach is using either their package database or their separate software version monitoring tool

How to materialize a version as well as "template-izing" the Dockerfile to cater for automated updates is also something that should be managed in the same context of opening a PR.

[jbergstroem]

Some updates as I will attempt this soon:

1. compare semver with dpkg --compare-versions "10.4.18-r0" "lt" "10.4.18-r1"
2. use their database to fetch upstream version
3. use local dockerfile to fetch release version
4. create a new PR with said change

[jbergstroem]

Just had another look at this. We can probably use renovatebot with annotations in the Dockerfile, alongside the repology data source. Much simpler!