Add scenario to create a commit via API

Add Create a commit scenario to the GPT.

POST /projects/:id/repository/commits - Create a commit with multiple files and actions
Prepare test data
Create a bug if the endpoint response time is above the main target(500 ms)

Source: https://gitlab.com/gitlab-com/Product/-/issues/1345#note_391571094

Edited Aug 21, 2020 by Nailia Iskhakova