fix(release): omit link_type when not specified uploading file

Description

Resolves #1154 (closed)

The GitLab API will set a link type to other when omitted. The cli is currently sending an empty string when a link_type isn't set, Causing a 400 error.

This MR omits the link_type rather than setting it to empty string. It also adds tests for the affected commands (release create and release upload).

Also have fixed some capitalisations inconsistencies in the output statements.

Related Issues

Resolves #1154 (closed)

How has this been tested?

Additional tests added for release create and release upload Manually tested

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)