[gpkg] Implement relationship creation, deletion and update support

[nyalldawson]

Relationships can only be updated to change their base or related table fields, or the relationship related table type. It is not permissible to change the base or related table itself, or the mapping table details. If this is desired then a new relationship should be created instead.

[rouault]

you may need to rebase on latest master, to get a fix that makes sure ASAN tests are based. Given that the "alpine" CI config fails with a hard crash, there might be some memory error somewhere. It could also come from a bad use of the API in Python, which can sometimes lead to crashes (like you work on a layer after destroying the dataset, or releasing it with ReleaseResultSet)

[nyalldawson]

@rouault

It could also come from a bad use of the API in Pytho

Got it -- I was reusing relationships which had been passed to UpdateRelationship, which takes ownership

[nyalldawson]

This will need squashing before merge, but I've left atomic commits here for review

[rouault]

For the linting issues, do you have pre-commit set up for your GDAL git checkout ? Cf https://gdal.org/development/dev_practices.html#commit-hooks . Once setup, git commit will re-format things automatically. It might be a bit surprising the first time, as it will return an error, but do the reformatting. You need to run git commit a second time, which will succeed then.

[nyalldawson]

For the linting issues, do you have pre-commit set up for your GDAL git checkout

I do now 😆