Support paginated list for job commits

[k1won]

My actions before raising this issue

• Read/searched the docs
• Searched past issues

Expected Behaviour

• Returns a paginated list result for the GET /api/jobs/{id}/commits request.
• If there are many changes to the job, it would be better to return only a few recent histories rather than returning all the contents at once.

Current Behaviour

• All commits are returned as a list at once.

Possible Solution

• modify the commits() method in JobViewSet class to support paginated list for job commits.

Steps to Reproduce (for bugs)

1. create some labeled shapes and save it
2. access to /api/jobs/{id}/commits with GET

Context

Your Environment

• Git hash commit (git log -1): be334fd
• Docker version docker version (e.g. Docker 17.0.05):
• Are you using Docker Swarm or Kubernetes?
• Operating System and version (e.g. Linux, Windows, MacOS): ubuntu 18.04
• Code example or link to GitHub repo or gist to reproduce problem:
• Other diagnostic information / logs:
  Logs from `cvat` container

Next steps

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[bsekachev]

It makes sense.
Also I would suggest to add a parameter page_size with ability to get all the commits when it is necessary.