Run all tests for checking new library version compatibility at once

[vjovanov]

What does this PR do?

Implements: #672

Implementation details

• Instead of returning a flat list of new versions, the fetchExistingLibrariesWithNewerVersions task now returns versions grouped by library.
• The workflow then gets this map, and spawns a new job for each key (in this case, name) in the returned map.
• For each spawned job, we are executing the tests for that library with newer versions sequentially using this script.
• Once the script finds first failing version, it returns list of all successful versions and a single (first) failing version.
• Later we process those results to create a PR for all successful versions and a ticket per library that contains information about first failing version.

[vjovanov]

Superseded by #708