Pin cdk-addons to the charm's channel and warn about cdk-addons deprecations

[addyess]

Addresses Issues

LP#2070379

Overview

Actively retire certain addons from cdk-addons by providing charm blocked state warnings for situations where users are using those features.

Details

• pinning the cdk-addons snap based on the charm's release channel. This will be determined from the charm branch the charm is built from (not the actual charmhub channel since that's not possible). The risk (edge,candidate,beta,stable) will match the configured snap channel.

example) So juju config kcp channel=1.28/beta sets the snap channel. If charm is built from the release_1.30 branch, then cdk-addons 1.30/beta will be installed along side the charm.

• Readds the openstack relation is added back in purely so the user can upgrade and see a blocked message
• Readds the config option enable-nvidia-plugin whose only acceptable value is "false" in order to dismiss blocked message

Associated PRs:

• cdk-addons is no longer a control-plane charm controlled by this library charm-lib-kubernetes-snaps#24
• Drop the cdk-addons label on ceph and keystone components cdk-addons#233

[kwmonroe]

lgtm

[kwmonroe]

clever!