[ui5-tooling-transpile] Provide custom path to tsconfig.json

[philippkolbe]

Problem
We are using the ui5-tooling-transpile-middleware to transpile our .ts files on build. We have several projects (i.e. one per app) and would like to share a tsconfig.json between all of those projects to avoid duplicating it.

We already only have one single shared .eslintrc.json between all apps. Not being able to share the tsconfig.json is especially annoying because the .eslintrc.json contains a path to a single tsconfig.json (overrides -> parserOptions -> project). This means that we need a single shared tsconfig.json anyways.

Sharing a tsconfig.json may seem a little counter-intuitive as it contains project specific configurations but we share code between different apps in a common library and therefore a shared tsconfig.json makes things easier.

Describe the solution you'd like
If we were able to provide a path to a tsconfig.json in the ui5.yaml specification we could share the tsconfig.json across apps.

Describe alternatives you've considered
We checked your library documentation but did not find any way to provide a path to a tsconfig.json. Copying all tsconfig.json files is possible but we would need to keep them in sync manually.