Reorganize workflow files

[haasad]

I'm tidying up the pipelines as part of #1094. This PR is mostly a cosmetic change, everything related to the github action pipelines is moved from the ci/ directory in the repo root to .github/ to have it all in one place.

The only exception is the conda recipe for the "stable" AB version which I moved to recipe/meta.yaml. Even if we don't actively use the stable AB version on the bsteubing channel anymore, this recipe is still the place where all dependencies and version pins are configured.

Checklist

• [x] Keep pull requests small so they can be easily reviewed.
• [x] Categorize the PR by setting a good title and adding one of the labels: bug, feature, ui, change, documentation, breaking, ci as they show up in the changelog
• [x] Link this PR to related issues by using closing keywords.
• [x] Request a review from another developer.

[coveralls]

coverage: 50.066%. remained the same when pulling e54e6450bda49b44bd4f650c752091e6ba581ec3 on reorganize-workflow-files into 7eebd42ea6da2c860ec8472561e13e837fcddc73 on master.

[github-actions[bot]]

This issue has been implemented in the new release of Activity Browser 🚀 (version 2.9.3), you can get the new version by updating Activity Browser.

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