Migration of registry-cloudwatch to AWS SDK 2.x

[PyvesB]

The AWS SDK for Java 2.0 reached general availability back in November (more information on their official blog post) and has de facto become the preferred way of integrating with AWS using Java.

Amongst other benefits, using it rather than the old version improves performance and allows to write cleaner code.

This pull request migrates the registry-cloudwatch implementation to the new SDK.

[shakuzen]

This would break all existing users of the CloudWatchMeterRegistry due to the constructor change. I don't think we want to do that in a minor release. Maybe it is better to make a separate module using the new AWS SDK v2 and mark the current one as deprecated for removal in our next major version.

[PyvesB]

Fair point. However, this would likely lead to some duplicated code. Is this temporary stateacceptable in your opinion, given that the old module will be deleted sometime in the future anyway? Or should we invest time in creating some sort of micrometer-registry-cloudwatch-common sub-project to extract as much common code as possible, used both by the micrometer-registry-cloudwatch and micrometer-registry-cloudwatch-v2 modules? Ideally, we would have to refactor again when the old module is deleted though.

[shakuzen]

I think duplicating the code will probably be simplest. We will just need to be careful that any bug fixes in one get ported to the other while we are supporting both.

[PyvesB]

Done. I called the new module micrometer-registry-cloudwatch2 to follow the same naming convention as with the Jersey implementation.

[shakuzen]

The new module should use a different package (most simply io.micrometer.cloudwatch2), but I can change this post merge. Thank you for contributing this.