Add new endpoints to ooniprobe for anonymous credentials

[LDiazN]

Create the new endpoints in ooniprobe for anonymous credentials

Those would be:

• /register to get a credential
• /submit to send a measurement, this could replace /report
• /update_credential for updating a credential (not yet implemented in the library)

Create this ONLY in the dev environment to test the client against it

[hellais]

This is completed and is currently deployed in the development environment