refactor: define a single method to remove entities from authz

[leafty]

Removing an entity from spicedb is equivalent to removing all relationships where the entity appears as a resource or as a subject. This means we should not need special cases for each entity type.

This refactor should also simplify the code for user removal (remove user entity + remove namespace entity). See #393.

[coveralls]

Pull Request Test Coverage Report for Build 11034384359

Details

• 28 of 33 (84.85%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.03%) to 90.429%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
components/renku_data_services/authz/authz.py	28	33	84.85%

Files with Coverage Reduction	New Missed Lines	%
components/renku_data_services/storage/blueprints.py	1	95.24%
components/renku_data_services/users/db.py	1	94.18%

Totals
Change from base Build 11033349401:	0.03%
Covered Lines:	9335
Relevant Lines:	10323

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💛 - Coveralls

[leafty]

Note: I am not sure if this will work for deleting users, as the permission check would probably fail.