What does this PR do?

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• Write the assignment reason from form routing or Salesforce routing to a field in Salesforce

https://www.loom.com/share/e1433e5847b6492d8e954ff1932f5b5d

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

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• Enable Salesforce on an event type and write to a field with the text value being {assignmentReason}

• Create a booking via Salesforce routing. The value should be written to the specified field

• Create a booking via form routing. The value should be written to the specified field

<!-- This is an auto-generated description by cubic. -->

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Summary by cubic

Added support for writing the latest assignment reason to Salesforce when syncing booking data.

• New Features
  • Fetches the most recent assignment reason for a booking and includes it in the Salesforce event payload.

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