CI | Publish Nightly of "Test AWS SDK Clients" Result in Slack

[shirady]

Describe the Problem

Add a step to publish the nightly test results of the job "test-aws-sdk-clients" in the Slack channel.

Explain the Changes

1. Add a step to message the job status - we temporarily message only success, then we will uncomment the condition and message only failures.

Issues:

• It was a gap of CI | Data Buckets | Test AWS SDK Clients #8847 and was mentioned as a part of issue CI | Add Notification in Slack Channels for Nightly Runs When Fails (GAP) #8905
• For more information, see this comment
• Now we're trying to test after merging and not use the secrets from a forked repo - see this comment.

Testing Instructions:

1. We will monitor the nightly run in the next days manually and check that the message was sent.

• Doc added/updated
• Tests added