feedback updating should not use a guessable identifier

[disperate]

After submitting a feedback on a page, it is possible to add a feedback_text.

This text is stored in the feedback model by making a POST request with the feedback pk as the identifier. This key is guessable and feedback from other users can potentially be manipulated.

Instead, a non-determinable identifier such as a uuid should be used.

[thibaudcolas]

Thanks for the report @disperate!