Persist winners for IRV contests

[vteague]

Persist IRV winners, which are currently returned by raire and may often be different from those generated by the contest counter.

Most likely, the best way to do this is with a new table. That table should include

• the contest name
• the winner
• an error, if any was returned by raire
• any warnings, e.g. time out trimming assertions.
• possibly an indication of whether there was an OK or an error response?

[vteague]

Consider concurrency issues, particularly the possibility that the GenerateAssertions endpoint might be required to run in parallel. Understand how to ensure that multiple concurrent runs do not interfere, either directly or because of database interactions. The ACVRUpload endpoint may be a good thing to emulate.

[vteague]

Answer: the AbstractEndpoint has a before() method which begins the transaction when the endpoint is first hit. The use of Persistence.flush() seems to be common, though in various places.

[vteague]

Decided to do this in the raire-service instead.