Limits how many times metainfo APIs can be called per second by project ID. If limit is exceeded, the API will return Unauthorized/Too Many requests.
Limit per second and the size of the limiter cache per project are configurable, as well as whether the limiter is enabled.
Tests added/updated for the new rate_limit field in projects table.
Tests added for exceeding limits and disableing limiter.
Change-Id: Ic8ad102de3b690a475809d4f684156d5715f20fa
