[FR]: custom tsconfig targets for different generated ts_project types

[jbedard]

What is the current behavior?

All ts_project targets use the same logic to find the tsconfig.

Describe the feature

The generated ts_project for tests (or custom targets) might want different tsconfig files. Maybe change js_tsconfig filename.json to js_tsconfig [target_group] filename.json to support overriding the default config per source group...