Error on large payloads from GitHub API

[steven-cd]

If a user attempts to submit a simulation through the API with a large config value, the request to the /repos/${repoOwner}/${repoName}/dispatches endpoint results in a 422 Unprocessable Entity, with the message "client_payload is too large.". The limit for the payload doesn't seem to be documented, but others suggest it's around ~70kB.

I can see three options here:

• We document some limit and reject requests bigger than it
  • Probably not viable for the work we're currently trying to do
• We compress (some of) the client_payload before sending it to GitHub, and then decompress it again in the model-runner
  • Should be straight-forward, although technically doesn't remove the limit entirely
• We write (some of) the client_payload into an object in the Blob Store, then send only the URL in the API request, and then fetch the file in the model-runner
  • Most future-proof solution, but does require the web-ui to write to the blob store, while previously it only read

[steven-cd]

A version using option 2, compression, has now been released, which should prevent this error in most cases. The last option is probably still the best however, and supports #44, so I'm going to leave this open until that is implemented.