Consolidate MR Ready and Code Conflict triggers as configuration
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## Consolidate MR Ready and Code Conflict triggers as configuration
### Summary
Consolidate the **MR Ready** (`merge_request_ready`) and **Code Conflict** triggers into a unified, configuration-driven approach for flows and agents, consistent with how other event triggers (e.g. MR Approved, pipeline events) are surfaced under `Automate > Triggers`.
### Background
Event triggers are being introduced incrementally for flows and agents. The **MR Approved** trigger configuration UI is tracked in [#600519](https://gitlab.com/gitlab-org/gitlab/-/work_items/600519). The **MR Ready** trigger backend was implemented in [#592454](https://gitlab.com/gitlab-org/gitlab/-/work_items/592454) (behind the `merge_request_ready_flow_trigger` feature flag, see [#598421](https://gitlab.com/gitlab-org/gitlab/-/work_items/598421)).
Rather than maintaining bespoke handling per trigger type, the MR Ready and Code Conflict triggers should be expressed as configuration so they appear and behave consistently in the **New Trigger** form alongside other trigger types.
### Problem
Without consolidating these triggers as configuration:
* Each trigger type requires custom UI/handling, increasing maintenance overhead
* The trigger selection experience is inconsistent across MR Ready, Code Conflict, MR Approved, and pipeline events
* Adding future triggers requires duplicating logic instead of extending configuration
### Proposed Solution
* Define **MR Ready** and **Code Conflict** triggers as configuration entries (consistent with the pattern used for MR Approved and pipeline event triggers)
* Surface both as selectable trigger types in the **New Trigger** form under `Automate > Triggers`
* Ensure each trigger persists and displays correctly when viewing an existing configuration
* Provide appropriate help text describing when each trigger fires
### Acceptance Criteria
- [ ] **MR Ready** and **Code Conflict** triggers are defined as configuration rather than bespoke handling
- [ ] Both triggers are available as options in the New Trigger form
- [ ] Selecting either trigger shows appropriate configuration UI and help text
- [ ] Each trigger is persisted and displayed correctly when viewing an existing trigger
- [ ] Behavior is consistent with other event triggers (MR Approved, pipeline events)
/cc Related to [#600519](https://gitlab.com/gitlab-org/gitlab/-/work_items/600519)
issue