Implement proper tagging strategy for docker images

[LesnyRumcajs]

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Issue summary

Right now we only tag whatever gets merged into main with latest. We should have more fine-grained control over this. To start with, releases should have their own tags. This should be probably implemented here. Next, the regular merges should get an additional tag - commit digest should be fine, or a combination of day and digest to make it more readable, e.g. forest:210629_26c85e8. The current version plus a number of builds since the last bump is also something I've seen in the past e.g. v0.2.2-42. Something to discuss.

The latest tag should then point to the most recent release tag.

Task summary

• [ ] Implement proper release tagging for docker images
• [ ] Implement proper merge commit tagging for docker images

Acceptance Criteria

• [ ] tags are properly added/updated on release job
• [ ] tags are properly added/updated on merge commit

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