doc: Update install instructions for deb and rpm

What

This MR removes the instructions for the serokell packages and provide instructions on how to install the rpm and deb packages now released in https://gitlab.com/tezos/tezos/-/packages/

Why

serokell packages are no longer developed, and deb and rpm packages are now distributed via https://gitlab.com/tezos/tezos/-/packages/

How

instructions on how to use these new packages is located here : https://chrispinnock.com/tezos/packages/

We might either link this page on the official documentation or adapt the official documentation.

Manually testing the MR

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