Use new version of Mozilla Observatory

[vlnst]

The previous version of Mozilla Observatory is is deprecated:

The previous version of HTTP Observatory is still available, however it is now deprecated and will soon be sunsetted.

The deprecated version will stop working in September 2024.

We should use the new version instead of previous or at least be prepared that it can stop working anytime now and the PrivateBin Instance Directory will not be able to supply users with the most recent data about the instance security rating

[elrido]

We will, once the API which we consume has been updated. As per their FAQ it hasn't yet: https://developer.mozilla.org/en-US/observatory/docs/faq#has_the_http_observatory_api_been_updated_to_use_the_new_tests

I checked their code (it's OSS) and the API seems to be identical and all we retrieve from it are the ratings, so the only change we should notice are that one day lots of ratings may change at once.