Add a settings cache context

Problem/Motivation

Some things are uncacheable because they depend on settings. For example, \Drupal\update\Access\UpdateManagerAccessCheck::access. This leads to issues like #3456128: Dynamic Page Cache uncachable on Drupal 10.3 with Admin Toolbar Tools and Update modules.

Steps to reproduce

Proposed resolution

Add a SettingsCacheContext

Remaining tasks

Test coverage

User interface changes

API changes

Data model changes

Release notes snippet