[Fleet] Indicate that Agent upgrades cannot be managed in Fleet

[ruflin]

Not all Agents managed can be upgraded upgrade might be disabled (see elastic/beats#21001 for more details). In Fleet, it must be indicated that these agents cannot be upgraded and upgrading must be disabled.

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[ph]

@hbharding @neptunian Could we find an easy way to define that in the UI?

[neptunian]

Currently in my local branch an agent is either upgradeable or not and if it is not it will not show that an upgrade is available. The only rule currently is if the agent is < kibana version. We can add more rules to this to cover the above scenarios. But do we want a separate state for these cases where it is out-of-date but cannot be upgraded due to these various reasons and do we want to communicate that to the user in some way? Do we still want to show the "Upgrade Available" indications, but disable the action upgrade button? But it might be confusing to filter by "Upgrade Available" and then not allow the user to upgrade or bulk upgrade in the actions. I am thinking perhaps in the Agent details page we can have more information about upgrading the particular agent. For now the easiest way is agents that fall into these scenario are just not upgradeable and we do not show the "Update available" for these.

[ph]

@neptunian This was implemented in Kibana?

For now the easiest way is agents that fall into these scenario are just not upgradeable and we do not show the "Update available" for these.

[neptunian]

Yes, there is a bug where I need to include the snapshots as not upgradeable through UI only but not part of this issue