Hard rate limits for document upload endpoint

[duckduckgrayduck]

Misconfigured scripts from end users with API access shouldn't fill up our Redis memory.

[allanlasser]

Rate limiting for a few kinds of behavior:

1. Bulk uploads
2. Solr indexing
3. OCR

We're leaving up to implementer where to layer the rate limit; sounds like we're in agreement it should happen at the point of HTTP method.

Discussion at tech team check-in