Cloudwatch logs driver: Ensure https prefix in endpoint and default to ACS provided endpoint if provided

[prateekchaudhry]

Summary

Context:
This PR builds upon previous work done to fix cloudwatch endpoints across different regions and partitions in following PRs

• Specifically set the CW endpoint when using awslogs as log driver for specifc regions #4143 - This change made agent pass in cloudwatchlogs endpoint for new regions/partitions, for which awslogs driver in Docker might not be able to resolve correctly
• Resolving cloudwatch endpoint for all regions #4191 - This open PR generalizes the above approach to all regions. The current PR is a further generalization of this PR, taking awslogs-endpoint - if available in ACS payload - into account

ACS payload

Implementation details

Testing

New tests cover the changes:

Description for the changelog

Does this PR include breaking model changes? If so, Have you added transformation functions?

Licensing

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