Increase Pipeline step limit beyond 10

Since as a customer, we are paying per 1000 compute minutes, it makes sense for those of us with very large test suites that want to parallelize them beyond 10 instances. Our specific use case is running browser-based integration tests across multiple versions of supported browsers, and the more we can parallelize, the merrier. Right now we're hard capped at 10 concurrent runs, which isn't enough for us to run all our tests in parallel.

Ideally we can run upwards of 50 concurrent instances, but ultimately I feel the limit should be higher than 10 with a reasonable cap.

The cap for a competing product, CircleCI, is 64 concurrent instances. I see no reason why Pipelines can't support at least 30+ concurrent steps.