fix(issue list): change output flag back to output-format

Description

Resolves #7491 (closed)

Changes the flag output for glab issue list back to output-format

As per !1031 (comment 1795691920) the flag output should have remained output-format

How has this been tested?

1. Checkout MR branch
2. make install
3. glab issue list --output-format ids
4. glab issue list --output-format json

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)
• Test gap