Throw exception on case-insensitive duplicate IDs

[kodumbeats]

MongoDB document keys are case sensitive, but MariaDB column names are not.

This PR adds a case-insensitive check when creating attributes/indexes or adding one to the queue, and will throw Utopia\Database\Exception\Duplicate if a match is found.

This PR also changes the default index on _uid for the MongoDB adapter to be case-insensitive.

Testing
Tests have been added to catch these exceptions.

Unanswered questions

• When adding attributes to a collection, the attribute document is appended to $attribute->getAttribute('attributes'), and when fetched, returns Document[] $attributes. However, when adding all attributes at once via createCollection, I receive just a plain array, not a Document. I had to hack around this problem, and I would like to not have to do this:

[eldadfux]

I think we need the same implementation for indexes as well if we don't have it yet.