[Serverless] add isError flag to channelMessage

[maxday]

What does this PR do?

This PR adds IsError field to the ChannelMessage structure. Before all message were set with status info but in some case, we want to tag message as error right away, for instance if we know that these are coming from stderr

Motivation

Set the correct level in message

Describe how to test/QA your changes

Unit test

Reviewer's Checklist

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• [ ] Changed code has automated tests for its functionality.
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[vickenty]

Would it make sense to instead expose the full status field, so that any of the available levels can be set?

[maxday]

Would it make sense to instead expose the full status field, so that any of the available levels can be set?

Sure! I can do the modification, the only downside of that is we could pass invalid status such as 'blablabla' WDYT?

[vickenty]

Good point! If there is no foreseeable need for more status options, what you have now in the PR might be better.