fix: catch ResourceNotFound error when adding code trigger in sam sync

[hawflau]

Which issue(s) does this change fix?

#6873

Why is this change necessary?

If a Layer is set with a S3 Location, sam sync throws an error and stack trace when trying to add a code trigger for that layer. (Same for Lambda Function as well). This is due to the Layer/Function with a S3 Location is considered as ResourceNotFound from the create_trigger's perspective.

How does it address the issue?

In the caller (_add_code_triggers of WatchManager), catch ResourceNotFound and issue a warning.

example:

2024-07-12 09:09:07,876 | The resource AWS::Serverless::LayerVersion 'MyLayer' has specified S3 location for ContentUri. It will not be built and SAM CLI does not support invoking it locally.                                                                                                                                                  
2024-07-12 09:09:07,877 | CodeTrigger not created as MyLayer is not found or is with a S3 Location.  

What side effects does this change have?

No

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.