Refactor environment variables validation

[NSeydoux]

This changes the environment validation so that booleans are used to flag env vars that should be validated, instead of a value of their type. Meaning

getBrowserTestingEnvironment({
      clientCredentials: {
        owner: { login: "", password: "" },
      },
    });

becomes

      clientCredentials: {
        owner: { login: true, password: true },
      },
    });
```, and the underlying environment variable get type-checked.

[ThisIsMissEm]

I think this may not do what we want, but I may be misreading the code.

[ThisIsMissEm]

Suggested change

	typeof process.env.E2E_TEST_OWNER_CLIENT_ID !== "string"
	typeof process.env.E2E_TEST_OWNER_CLIENT_ID !== "string" && process.env.E2E_TEST_OWNER_CLIENT_ID !== ""

We should be checking that we actually have a valid value set.

[NSeydoux]

Fixed in db46a19.

[ThisIsMissEm]

This'll do for now, though I was looking at these:

• https://www.npmjs.com/package/yup-env
• https://www.npmjs.com/package/envalidate
• https://www.npmjs.com/package/zod
• https://github.com/lostfictions/znv

Which might be more maintainable in the future, as the index.ts file is getting a bit unwieldy.