Add support for test versions

[danitseitlin]

There is a need for the ability to release "test" versions, the most common intention is to create a test release version on PR changes.
When a version already exists, it should remove it and create a new one.
Add the ability to remove the test version after merge.

Each test version will be only available on pull_request GitHub action event.
When deployment_type is "test" it will do the following on a pull_request event only:

1. If the test version does not exist, it will create one, the version name would consist of the prefix 'test' and the branch. i.e. test-fix-issue-with-stats
2. If the test version exists, it will remove it and deploy a new one.

When the even will be push, the test version will be removed if it exists.