Provide CLI option for `tsconfig.json` path to allow different config per env

[hamish-later]

Please write a user story for this feature

Follow the form

As a role, I want feature so that reason.

Example:

As an addon publisher, I want tobe able to precompile my addon's typescript into js, so that my consumers can use my code, regardless of whether their app is written in typescript

As a developer, I want to be able to specify different tsconfig.json file paths upon serving my app, so that my team can extend our base config and override environment-specific TypeScript options. For example, exclude paths and includes related to testing from our base tsconfig.json, but include them in tsconfig.test.json.