feat(mr create): Add --signoff option

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Description

These changes allow for a user to append a --signoff option to existing glab mr create commands and have a DCO appended to their MR Description.

Related Issues

Resolves #7569 (closed)

How has this been tested?

Ran tests locally on my machine via make test, along with gofumpt linter (and golangci-lint).

Logs: test-output.log

Additionally, created MRs to a local project and tested --signoff with and without templates. Host environment: Apple M1 on Sonoma 14.5

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

Signed-off-by: Derek Barbosa derekasobrab@gmail.com