server/tests: enable cockroachdb in the pytest suite

[sassela]

This should be a timeboxed exercise to see whether we can easily run our full existing Postgres test suite against a CockroachDB. The effort can be a hack / throwaway.

We want to be able to run the entire Python integration test suite (including schema, queries, mutations and subscriptions) against CockroachDB, to better understand which features are supported out the box, and which will need extra work to support.

This issue may involve following these docs to test against CockroachDB, similarly to how we currently do for Citus. In short:

• launch and cleanup a cockroachDB server
• introduce a cockroachdb pytest fixture
• pass the fixture into every test class (I believe we can specify a test fixture per module, but will share a link to the docs as I find it)
• introduce setup/teardown files for each test, or introduce a helper method to minimise or remove the need for duplication

We shouldn't run these tests in CI right now, assuming at least some of them may fail anyway.

[sassela]

Discussed after standup: this should be (at least partially) unblocked by this PG wire protocol fix.

[sassela]

tested in api-tests instead, closing https://github.com/hasura/graphql-engine/commit/4237c5641944e8256b65b9305775c4b764c5fd4d