Details pane against unavailable Pro updates is misleading

Indeed the UI there is confusing. When the system is not attached to Ubuntu Pro the updates are unknown to apt. We build the UI by getting a list of binaries from 'pro security-status' but we didn't include extra logic to adapt the 'details' section. The 'available' version comes from apt and in this case there is no update.

We could probably also get the version for the pro command to fix the 'available version' information but I'm unsure if we have a way to have access to the changelog to display actual content.

@Design, what would we recommend doing? Should we just fix the version even without changelog description? Hide the section? Add some text explaining how the Pro updates are different?

Bringing the side conversation here:

- the Pro Client has https://canonical-ubuntu-pro-client.readthedocs-hosted.com/en/latest/references/api.html#u-pro-packages-updates-v1 , which shows the same updates in security status but versioned and machine consumable (security status --format json will be deprecated at some point in time, when we are sure the APIs are sufficient)

- There is not currently a way of getting the changelogs for the ESM versions, and if there is and I don't know about it, not when you are unattached. So the good way to go would be replacing the changelog entry with this explanation about how Pro works a little different. If you want to include technical details from our side in this explanation I'm glad to help.