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This will create a feature request which anybody can view and comment on.

Please describe your requested enhancement. Good feature requests will solve common problems or enable new use cases.

What you would like to accomplish:

We have an automated process that kills bigquery job if certain parameters are met. While this works well from the admin perspective we'd like to provide a string in a param `message` that will be presented to downstream users in their error logs.  Currently all that occurs is that downstream users receive a `Exception: 200 Job execution was cancelled: User requested cancellation; reason: stopped, message: Job execution was cancelled: User requested cancellation` which isn't helpful as it doesn't say who or why cancelled the job. The optional message param would allow communicating both of these.

How this might work:
Add a message param to https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs/cancel


If applicable, reasons why alternative solutions are not sufficient:
1) Manual communication does not scale effectively
2) Pointing users to another system's logs to read why their job was cancelled is time consuming
3) The current message is insufficient as it does not provide a way for admins to tell downstream users why their query was cancelled  `Exception: 200 Job execution was cancelled: User requested cancellation; reason: stopped, message: Job execution was cancelled: User requested cancellation`

Other information (workarounds you have tried, documentation consulted, etc):
N/A