Add update original message to destination configurations

[nzur-newrelic]

Description

Please include a summary of the change and which issue is fixed (if relevant). Added a new field to destination block called update_original_message which for the moment only works for Slack channels. Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] This change requires a documentation update

Checklist:

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• [x] My commit message follows conventional commits
• [x] My code is formatted to Go standards
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes. Go here for instructions on running tests locally.

How to test this change?

Please describe how to test your changes. Include any relevant steps in the UI, HCL file(s), commands, etc

The test is solely minimal to see that a workflow can be created with the field, as it requires a slack channel for the field to change.