FE: Allow users to unmap an available agent to a group

MR: Add Map/unmap agent actions to Agent auth UI (!154303 - merged)

Description

As a group owner or instance admin, I want to unmap an agent from a group so it cannot be used by developers to create Remote Development workspaces.

Acceptance Criteria

• This action is only allowed to group owners and instance administrators.
• This action is only available on mapped agents.
• The action appears as a button next to an agent in the "All agents" and "Allowed agents" table. The button label is "Block" indicating that an agent won't be available to use to create Workspaces.
• Ensure that modal is properly displayed: #440738[b1_workspacesettings_unmap.png]
• Ensure agent is removed from table.

Technical Requirements

• The "Block" button should display a loading indicator and become disabled while the mapping operation is in progress.

Design Requirements

Design reasoning here