Key integration

Thank you for providing a patch! Since patches are no longer tested, we need a merge request.

-        "drupal/mailsystem": "It provides an administrative UI and developers API for managing the used mail backend/plugin."
+        "drupal/mailsystem": "It provides an administrative UI and developers API for managing the used mail backend/plugin.",
+        "drupal/key": "^1.19"

As with the existing suggestion, the content of the key is a description of the package or a description of why the package is suggested, not the package version to use.

I am working here.

Created MR 42 for 2.0.x-dev branch.

Tested the MR. The key integration with the Graph mail module seems to work fine.
Created a key of type Graph Mail and configured the graph api mail settings to work to with the key created. Used dummy values for testing. All the comments on the MR also seems to be addressed. Attaching a video for reference and moving it to RTBC.

Actually, since there are 59 sites using the 2.0.0-alpha7 release, I would prefer the changes are backward compatible, which means the Key module cannot be a hard dependency, or those sites will not be able to update.
I know that alpha releases do not need to be backward compatible, but I would rather avoid disruptions on those sites.

My idea was to wait to create a pre-release, to avoid such changes, but the pre-release was created, and we cannot turn back.