chore(main): release 2.20.0

[release-please[bot]]

:robot: I have created a release beep boop

2.20.0 (2024-01-25)

Features

• Add new types QueryMode, QueryPlan, ResultSetStats (#512) (b399c4c)

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[parthea]

Adding do not merge as certain changes from https://github.com/googleapis/python-datastore/pull/512 may be reverted. Googlers see b/321794555

[parthea]

Closing release PR which contains obsolete release notes