ci: Add manual backport trigger via workflow_dispatch

[Yaminyam]

This pull request introduces changes to the GitHub Actions workflow to support manual dispatch for backporting pull requests. The most important changes include adding inputs for the workflow_dispatch event and modifying the jobs section to handle commits based on the event type.

Enhancements to workflow dispatch:

• .github/workflows/backport.yml: Added workflow_dispatch event with an input for pr_number to allow manual triggering of the backport workflow.

Modifications to job steps:

• .github/workflows/backport.yml: Updated the matrix output to handle commits from either the push or workflow_dispatch events.
• .github/workflows/backport.yml: Added conditional steps to get commits based on whether the event is a push or workflow_dispatch.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version

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.github/workflows/backport.yml:36

• The command assumes that the commit message contains the PR number in the format (#PR_NUMBER). If the commit message format does not follow this convention, the backport workflow will fail to find the correct commit. Consider adding a more robust method to identify the commit associated with the PR.

commits=$(git rev-list main --grep="(#${pr_number})" -n 1 | jq -Rc '[.]')

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