Add ability to customise test command

[danhawkins]

Is your feature request related to a problem? Please describe.
In some cases, tests execute via a wrapper, some examples are encore.dev uses encore test and in this persons case the are using doppler, these wrappers are required for various reasons.

Describe the solution you'd like
Just like there is an option to configure testFlags, it would be excellent to be able to specify testCcommand or similar, allowing the user control of the process called to execute tests, with the assumption that the called script / binary is compliant with the arguments being passed

Describe alternatives you've considered
Right now, I'm running using https://github.com/cortesi/modd without IDE integration for tests that need the wrapper

Additional context
N/A