feat/variable-export

Description

Related Issues

Resolves #1218 (closed)

• Introduces a "export" subcommand in the "variable" namespace.
• Allows for exporting a paginated result of the ci/cd variables to json

How has this been tested?

• There are no Integration/Unit tests, I am willing to add some, if there is interest
• I tested it just by executing the commands with my Gitlab.com account

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)