Update API to deploy separate endpoints by run ID

[jeancochrane]

This PR updates api.R to deploy multiple /predict endpoints, one for each of a set of valid run IDs. The new API structure looks like this:

• POST /predict: Predicts with a default model, configured via the AWS_S3_MODEL_RUN_ID environment variable
• POST /predict/<run_id>: Predicts with a model determined by the run ID passed to the endpoint

Maintaining a POST /predict endpoint that falls back to a default model should allow us to deploy this change without disrupting the operation of the workbooks that Valuations is currently using for desk review.

Closes #1.

Deployment steps

• [x] Notify Valuations and IT that we are deploying changes to the API
• [x] Merge the PR
• [x] Pull the latest image on the server
• [x] Make sure the env vars are up to date
  • [x] Rename AWS_S3_MODEL_RUN_ID to AWS_S3_DEFAULT_MODEL_RUN_ID
  • [x] Remove AWS_S3_DVC_BUCKET
  • [x] Remove AWS_S3_MODEL_YEAR
• [x] Try removing privileged: true
• [x] Restart the compose process and see if it works
• [x] Modify and reupload any API workbooks that need to change

[jeancochrane]

Ready for another look @dfsnow!

[jeancochrane]

@dfsnow I think we should get one last look at this, unfortunately I had to make a lot of changes since the last round of review!