Don't send anonymous consent to the ConsentProxy

[oliverturner]

Context

Anonymous users store a record of their consent in a local cookie rather than on the Consent Store, so this PR returns early from sendConsent (i.e. before making the POST request) if the fow prop is undefined.

This change avoids the need for the App to hard-code an API key.

Planned work

• Here:
  1. A variant of this unit test to validate that the expected callbacks are run on form submission if fow is undefined
  2. An integration test that checks that the success alert is displayed on form submission when fow is undefined
  3. Optionally a snapshot
• FT App:
  1. Pull in an updated version of this component
  2. Make the request for FoW data conditional on whether the user is authenticated (allowing the removal of the hard-coded API key)
  3. Ensure that the value of the fow prop passed to this component is appropriate to the type of user (i.e. undefined for anon, defined for authenticated)