Use testcontainers to spawn MySQL server container in unit tests. #1457

[arthurschreiber]

Description

This PR is a duplicate of https://github.com/github/gh-ost/pull/1457, as https://github.com/github/gh-ost/pull/1457 targeted the wrong branch.

In case this PR introduced Go code changes:

• [ ] contributed code is using same conventions as original code
• [ ] script/cibuild returns with no formatting errors, build errors or unit test errors.