Make source param required while calling the server endpoint. (task)

Note: there are still some places where source is optional but it is used in a different context - for now we care only about making it required while connecting with the keyserver, but if it is signification can be refactored in the future to make source required in remaining places.

1. Running flow check.
2. Checking all callers of resolveInvalidatedCookie - it's called only by fetchNewCookieFromNativeCredentials and source was required there previously and everywhere fetchNewCookieFromNativeCredentials is called source is passed explicitly from loginActionSources.