Deprecate the Olivero theme

Problem/Motivation

Deprecate extension Olivero. See Remove a core extension and move it to a contributed project of the deprecation policy.

The removal of Olivero was approved in #3590816: [policy, no patch] Deprecate Olivero and move to contrib.

This is postponed until all usages of this extension outside of the extension itself is properly handled.

Remaining tasks

This is the actual deprecation and is limited to the following tasks. See the parent issue for the full process.

1. Create a section on Deprecated and obsolete modules and themes to provide recommendations for sites using extension Olivero. The recommendations are to include instructions for sites using the extension and for contributed projects that depend on then extension.
2. Add the following to the extension info.yml file

lifecycle: deprecated
lifecycle_link: https://www.drupal.org/node/3223395#s-olivero

3. Add #[IgnoreDeprecations] to all tests in the extension.
4. Add a change record and include a link the the doc page.
5. Deprecate any library that is only used by the extension.
6. Do a thorough search of core for any remaining references to the extension. If references are found, outside of the extension, then creates issues to remove the references.

Release notes snippet