Create triggers for project item consumers

What does this MR do and why?

Create triggers for project item consumers

Get the service account from the parent item consumer, and create a flow trigger with the event types passed by the user.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

0. Enable the ai_catalog_flows and global_ai_catalog flags
1. Create a flow:

mutation {
  aiCatalogFlowCreate(
    input: {name: "Test flow", description: "Trigger test flow", projectId: "gid://gitlab/Project/1000000", public: true, definition: "version: v1\nenvironment: ambient\ncomponents:\n  - name: main_agent\n    type: AgentComponent\n    prompt_id: test_prompt\nrouters: []\nflow:\n  entry_point: main_agent"}
  ) {
    errors
    item {
      id
    }
  }
}

2. Attempt to create an item consumer for the flow with a trigger:

mutation {
  aiCatalogItemConsumerCreate(
    input: {itemId: "gid://gitlab/Ai::Catalog::Item/<REPLACE WITH ID ABOVE>", target: {projectId: "gid://gitlab/Project/1000000"}, triggerTypes: ["mention"]}
  ) {
    itemConsumer {
      id
    }
    errors
  }
}

You should see the error "Item must be added to the top-level group before adding to the project"

3. Try creating it along with triggers for the group:

mutation {
  aiCatalogItemConsumerCreate(
    input: {itemId: "gid://gitlab/Ai::Catalog::Item/<REPLACE WITH ID ABOVE>", target: {groupId: "gid://gitlab/Group/1000000"}, triggerTypes: ["mention"]}
  ) {
    itemConsumer {
      id
    }
    errors
  }
}

4. You'll now see the error "Flow triggers can only be set for projects"

5. Create the item consumer for the group without triggers (NOTE: You'll need to check out the branch 578532-be-support-adding-a-flow-to-a-group for this step, as that creates the service account, then switch back):

mutation {
  aiCatalogItemConsumerCreate(
    input: {itemId: "gid://gitlab/Ai::Catalog::Item/<REPLACE WITH ID ABOVE>", target: {groupId: "gid://gitlab/Group/1000000"}}
  ) {
    itemConsumer {
      id
    }
    errors
  }
}

6. Now finally add it to the project, with triggers:

mutation {
  aiCatalogItemConsumerCreate(
    input: {itemId: "gid://gitlab/Ai::Catalog::Item/<REPLACE WITH ID ABOVE>", target: {projectId: "gid://gitlab/Project/1000000"}, triggerTypes: ["mention"], parentItemConsumerId: "gid://gitlab/Ai::Catalog::ItemConsumer/<PARENT ITEM CONSUMER CREATED ABOVE>"}
  ) {
    itemConsumer {
      id
    }
    errors
  }
}

Find the item and confirm it has the right flow trigger:

i = Ai::Catalog::ItemConsumer.last
i.flow_trigger
i.event_types # [0] which is "mention"
i.flow_trigger.user # Service account `@ai-trigger-test-flow-gitlab-duo`
i.project # Project you added the flow to

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Related to #578349 (closed)