Add ability to delete/disable/enable an agent at the Project level

As part of AI Catalog, we want to move the agent deletion from the Explore section to the Project>Automation section.

See issue Add "Enabled" / "Owned by this project" nav tab... (#573249) for context on list tabs at Project level:

• Enabled agents (itemConsumers): When viewing an enabled agent, the action to disable it is available in the top right corner with other available actions. This effectively removes the item consumer. The agent would now be visible from the second tab. If the user deletes the agent, the itemConsumer in the current project is deleted alongside the agent.
• Disabled agents (second tab): When viewing a disabled agent, the action to enable it is available in the top right corner with other actions available. This creates an itemConsumer for this agent in the current project. The user can also delete the disabled agent.

See issue https://gitlab.com/gitlab-org/gitlab/-/issues/575127+ for backend dependencies.

These actions should be made available behind :ai_catalog_item_project_curation feature flag.