add new pretty url for debian repositories

What

This MR updates the documentation for debian packages.

It also use the new url https://packages.nomadic-labs.com for debian repositories.

Why

How

Manually testing the MR

check if the new url works as advertise an check if the doc is correctly generated. https://tezos.gitlab.io/-/tezos/-/jobs/8030182534/artifacts/docs/_build/introduction/howtoget.html#installing-binaries

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR