Epic: Enable EP Merge for single contention new claims

[amylai-va]

The EP400 Merge MVP was narrowly scoped to work on claims for increase (with only one condition).

As a next step, we'd like to expand this functionality to new claims (but still with one condition).

User Story

As a VSR, I want single contention new EP400 claims to be combined with the Veteran's existing pending claim, so that I do not have to manually combine them.

Acceptance Criteria

(Pulled from: https://github.com/department-of-veterans-affairs/abd-vro/issues/2052)

1. If the claim meets all eligibility criteria, send it to VRO EP Merge and https://github.com/department-of-veterans-affairs/abd-vro/issues/2053
2. If the claim does not meet all eligibility criteria, the no action is taken and the claim will be processed normally
3. [TBD] -- launch plan? (all at once? phased rollout?) 🚀 Launch Plan here 🚀
4. [TBD] -- comms strategy? (who needs to know? are there SME's we should consult?)
5. [TBD] -- testing strategy? See launch plan above

Eligibility Criteria

(Pulled from: https://github.com/department-of-veterans-affairs/abd-vro/issues/2052)

• The EP400 is a single contention new claim
• The contention on the EP400 has a contention classification
• The Veteran only has 1 pending rating claim (relevant rating EPs are: 010, 110, 020, 030, and 040's + any incremental EPs like 031s and 041s)
• The pending claim is an EP010, 110, or 020

Not included in this work

We're not working on any claim here with multiple conditions. That is covered here: https://github.com/department-of-veterans-affairs/abd-vro/issues/3001

Notes about work

Links

• Milestone: EP400 Merge MVP
• Milestone: EP400 Merge Post-MVP

Tasks

### Linked Issues
- [ ] https://github.com/department-of-veterans-affairs/abd-vro/issues/3035
- [x] Draft launch plan for EP merge post-MVP updates (new/multiple contention claims)

[dfitchett]

Couple of notes about this work:

• EP Merge should be able to handle contentions with NEW status without any changes. In fact we already have a unit test for EP400 that covers a claim with a single new contention.
• vets-api:
  • Contention classification already supports NEW contentions. The eligibility to send requests to EP Merge via prepare_for_ep_merge! needs be updated to remove the increase_only? criteria. It would also be beneficial to provide metrics on the type (new or CFI) of contentions submitted to EP Merge.

[dfitchett]

@nanotone we should put this behind a feature flag so that we can test in staging first.