db2 for i support

[sdepold]

Mark: Rik reviewed the PR and gave feedback. Remaining questions

• CI/CD strategy: Run smoke tests every so often on main only. Let's do it afterwards.

Running all integration tests takes roughly 20 hours. Majority of tests are working fine. One final commit will come in and then it should be ready.

Mark: Work on the smoke test in a future PR and notify the slack channel in case of failure (maybe changelog).
Please disable the integration tests for db2 for i in the PR.

Did we figure out why db2 fails randomly: Once the PR for db2 for i is completed, Mark will look into it.

Update March 23rd:
PR has landed, release under some v7 alpha version
Mark wanted to work on the integration. No update yet.

Update April 21st:
To be confirmed: Kevin Adler is taking over the work.
@sascha configure the Github Action. Double check with Mark + Kevin what is happening with the flaky db2 tests.

[sdepold]

Todo: Print warning when experimental dialects are used (snowflake and db2 for i).