Xcode13 support, Updated documentation and a few new features

[ecamacho]

• Bumps dependencies to be able to build in Xcode 13
• Adds more documentation about the new Statistics Jobs used by the Backstage plugin
• Adds a new environment variable REDIS_CONNECTION_TIMEOUT to specify the Redis connection timeout. Useful when it takes some seconds to connect to redis
• Adds a new /v1/health/jobs health check endpoint to verify that the Backend can connect to Redis. Useful in cases where the backend disconnects.
• Fixes some Statistics tests that were failing
• Regenerate the list of tests so all are run in CI
• Bumps nokogiri version to fix a vulnerability

[polac24]

Seems that tests are failing due to off-by-one mistake.