Scheduled weekly rebuild of Docker image of latest release

[juhoinkinen]

It might be a good idea to rebuild Docker images of "maintained" releases regularly for package updates. We could consider only the most recent release to be "maintained" in this sense (for now at least).

This PR adds a weekly run GH Actions workflow, which

1. checkouts the git tag of the latest release
2. builds image and tests it with pytest
3. pushes the image

Currently the image is pushed to my DockerHub account, and the schedule does not work because the (cron) workflow is not in the main branch.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (f39d494) 99.67% compared to head (3ec1d4b) 99.67%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #713 +/- ## ======================================= Coverage 99.67% 99.67% ======================================= Files 89 89 Lines 6380 6380 ======================================= Hits 6359 6359 Misses 21 21 ```

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[juhoinkinen]

Closed in favor of #715.