Add AWS SNS event callback during cluster setup

[rkenmi]

Why are these changes needed?

This PR adds a SNS event callback for each Ray cluster setup event. Tested with ray up, ray exec.

TODO: need to add unit tests

To configure, the cluster_notifications should be added as a field under provider (with type aws)

cluster_notifications takes the following arguments:

• sns_topic_arn: ARN for the Amazon SNS topic.
• parameters: Arbitrary key-value parameters that you want to include into the body of each SNS notification. This might be useful, if for example, you need to pass in additional metadata for a particular Ray job, such as the job ID.

Example:

# Cloud-provider specific configuration.
provider:
    type: aws
    ...
    # If specified, publishes head node cluster setup events to an SNS topic.
    # Additional message parameters specified here will be included in every SNS notification.
    cluster_notifications:
        sns_topic_arn: "arn:aws:sns:us-west-2a:012345678901:01234567-89ab-cdef-0123-456789abcdef"
        parameters:
             jobId: exampleRayJobId
             createdTimestamp: 123456789
             ...

Related issue number

Checks

• [x] I'm working against the latest source on the experimental branch.
• [x] I've run scripts/format.sh to lint the changes in this PR.
• [ ] I've included any doc changes needed.
• [x] I've made sure the tests are passing. Note that there might be a few flaky tests.
• Testing Strategy
  • [ ] Unit tests
  • [ ] Release tests
  • [ ] This PR is not tested :(

License

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

[Zyiqin-Miranda]

Would you mind open this PR against the experimental branch instead of main?

[rkenmi]

Closing the PR and opening a new one rebased on the experimental branch.