Automatize release checklist issue creation

What does this MR do?

Adds one more improvement in the template and a script for automation of issue creation.

How it works?

1. Export GITLAB_API_PRIVATE_TOKEN variable, that contains your Private Access Token

2. Execute make prepare_release_checklist_issue,

3. Answer few questions:

   Major version number:
   10
   Minor version number:
   8
   GitLab.com handle of the release manager:
   tmaczukin
   ID of the Release Blog Post MR:
   12345
   Deadline for adding Runner specific content to the Release Blog Post:
   2018-05-13

4. Open the printed URL and read the filled issue :)

Why was this MR needed?

Helps GitLab Runner's release manager prepare the checklist issue ;)

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?