Allow Guzzle 8 in Drupal 11

Problem/Motivation

In #3612544: Update to Guzzle 8 we added support for Guzzle 8 to Drupal 12. We should see if we can backport the changes to allow both Guzzle 7 and 8 in Drupal 11, as there is a possibility that Guzzle 7 will be end of life before Drupal 11 is end of life.

Steps to reproduce

Proposed resolution

Backport the changes, run tests on both branches, see if supporting both is viable.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet