[Fleet] Disable Delete Policy button for Managed Policies

[Zacqary]

Policies marked with the is_default flags have their Delete button grayed out in the UI. Policies marked with is_managed also cannot be deleted, but the Delete button is available.

Clicking Delete will throw an error, but we should disable the button so that the user can't even get that far.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[elasticmachine]

Pinging @elastic/fleet (Feature:Fleet)

[nchaulet]

Should we disable deleting the default fleet server policy too (is_default_fleet_server flag on the policy) ?

[Zacqary]

@nchaulet Yes definitely. I just tested it and it looks like the Default Fleet Server policy can be deleted. That's not good.

[jfsiii]

I believe this is covered under #91906

I removed it from the settings tab on the policy details view in #96337 (still draft atm)

I wondered about the Default Fleet Server Policy when I was doing that. I can update it in that PR

[hbharding]

Hey just setting this. As John mentioned, these (and many other) actions related to hosted agent policies are already accounted for. We decided to hide (rather than disable) the actions since there is nothing the user can do to enable them. Related to this, I opened an issue so that we do the same thing for policies that are marked is_default #95226

[ruflin]

Closing as I assume this is covered in #91906.