[FEATURE] Create integration with Bitrise

Bitrise offers easy-to-use "steps" to be included in their CI pipelines. This could potentially make it easier for people to adopt Reassure. Especially if they're on paid plans, in which case Bitrise promises to deliver dedicated machines spawning VMs that are exact copies of each other (which we could leverage for sharding tests in the future).

Let's explore creating such a step. Here's relevant docs: https://devcenter.bitrise.io/en/steps-and-workflows/developing-your-own-bitrise-step/developing-a-new-step.html