feat: add revert-specific MR description template

Enhance patch MR template to distinguish revert operations:
- Add conditional logic to show revert context in MR description
- Parse original patch ID from RelatedTo field
- Use Origin field to detect revert patches
- No signature changes to createPatchMergeRequest

MR descriptions now show:
- Standard patches: 'adds the patch ID...'
- Revert patches: 'reverts patch X by deleting it and creating...'

Verified: MR
https://ops.gitlab.net/gitlab-com/gl-infra/cells/tissue/-/merge_requests/1142
shows correct revert description

Related: https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/21502