[schema] use json to serialize constraints Require yams 0.43: constraints are serialized to json, which means we need to recreate the actual checks in the database on upgrade. Temporary deps in tox.ini to pull respective changes in yams.

Release notes
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.. toctree::
    :maxdepth: 1

    3.22
    3.21
    3.20
    3.19
    3.18
    3.17
    3.16
    3.15
    3.14