Add unit test for sql domain store

[Shaddoll]

What changed?

• Add unit test for mysql configstore
• Split sql statements into a different file

Why?
To improve code quality

How did you test it?
unit test

Potential risks

Release notes

Documentation Changes

[3vilhamster]

LGTM.
Though, I would like to have error cases separated from non-error. That makes test setup easier and makes easier to reason on missing test coverage.
Something like:

TestGetMetadataSuccess()

TestGetMetadataFailures()