Temporarily update which special issue the EP Merge App removes when some steps fail

[amylai-va]

Typically, when certain steps within the merge process fails, we need to remove the EMP special issue. This ticket tracks work to temporarily change the special issue that we remove from EMP to RRD so that we can proceed with EP400 e2e testing in va.gov staging / VBMS UAT.

Acceptance Criteria

• when a step fails in the merge process and the special issue needs to be removed from the EP400 contention, the EP Merge App removes the RRD special issue from the contention

Notes about work

• At the moment, EP400 claims are unable to be established in va.gov staging with the EMP special issue since it's not a valid special issue identifier according to EVSS
• EVSS is planning to add EMP as a valid special issue and estimates that it will be available in PINT/staging on February 29th
• This ticket will enable us to proceed with EP400 e2e testing in the meantime

[dfitchett]

This implementation that was completed in the workaround allows us to change the special issue code via environment variable or just default to EMP. So when we do the deployment, we can just have VRO set an env variable for us to change it to RRD. This also renders #2647 unnecessary.