Configure EnableThreadSafetyChecks for functional tests too

[Piedone]

Is your feature request related to a problem? Please describe.

The new YesSql option, EnableThreadSafetyChecks, is enabled for some integrations tests. This is good, because it'll make issues like #15794 and #15628 more apparent by directly failing the tests. However, this is also needed for functional tests for the same reason.

Describe the solution you'd like

Most possibly, we need to pass a parameter to the web app when running it here, and bind it to EnableThreadSafetyChecks out of the box. Then, we also need to update the default appsettings.json with an example (but it should still be off by default).

Describe alternatives you've considered

I thought about not binding the config by default, but then we'd need to do some testing-specific change in the codebase still.

[Piedone]

Related: #12834.