Future-proofing privacy considerations of New API feature to identify feature support per operator

[sandandsnow]

Making a note here for completeness (see also discussion at w3cping/privacy-request#156) to ensure:

(1) the spec explicitly communicates that this capability doesn't add entropy, that it is just a more convenient way of discovering feature support information that can be inferred from the OS and browser version already

(2) To ensure the extension point for privacy controls are in place to prevent the capability from being used in the future for fingerprinting, etc.

[anssiko]

Reopening. We want to ensure the specification is cohesive with respect to its privacy posture, and thus we will revise the privacy considerations in the light of new information. This work is tracked in #886