Add a pipeline to produce major release builds

[Mikhail Lopatkin]

The new pipeline should run manually only on master branch and:

1. Build a non-snapshot release off the tip of the master branch and publish it
2. Add a proper tag to the commit from which release was built
3. Increment major version (e. g. 0.20 → 0.21)

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[Mikhail Lopatkin]

Thinking about it a little more, I decided that I want to add tag myself, in a non-automated fashion. I'll also do major version increment manually. Therefore, only non-snapshot build out of tag is needed.

[Mikhail Lopatkin]

Tag-based pipeline added in PR #23