test(referential-action-set-null): add SQL tests for 1:1, 1:n relations with SET NULL referential actions

[jkomyno]

To run tests:

• cd package/client
• pnpm test:functional referential-action-set-null/tests_1-to-1.ts
• pnpm test:functional referential-action-set-null/tests_1-to-n.ts

These tests expect the following environment variables (which are already used by the test codebase):

• TEST_FUNCTIONAL_MYSQL_URI
• TEST_FUNCTIONAL_POSTGRES_URI
• TEST_FUNCTIONAL_COCKROACH_URI (unnecessary when TEST_SKIP_COCKROACHDB is defined)
• TEST_MSSQL_URI (unnecessary when TEST_SKIP_MSSQL is defined)

Outcome

• For both 1:1 and 1:n relations:
  • postgres doesn't validate DDL statements that set a SET NULL referential action on a foreign key constraint whose referenced column (or one of the referenced columns) is NOT NULL, all other database throw a validation error in this case.
  • postgres fails at runtime with a not-null constraint violation error when UPDATE / DELETE statements trigger the SET NULL referential action on a column defined as NOT NULL
• sqlserver fails at runtime on 1:1 NULL relations because NULL conflicts with UNIQUE indexes in that particular database

TODOs

• fix cockroach and postgres in insert + update + delete tests
• fix Migration engine error: db error: ERROR: database “PRISMA_DB_NAME” is being accessed by other users
• Skip miniproxy
• Fix buildkite CI
  • on postgres: error: database "PRISMA_DB_NAME" does not exist
  • on sqlserver: Login failed for user 'sa'.
• (LOW PRIORITY, can be done after we go GA with referential integrity) define TEST_FUNCTIONAL_MARIADB_URI in CI as "mysql://root:root@localhost:4306/PRISMA_DB_NAME"