Improve CloudTrail Metrics / Alarm definition

[lgallard]

Describe the Feature

Improve CloudTrail Alarm definition, having just one place to enhance reusability.

Another improvement is to change the input layer for its purpose, such as setting CloudTrail bucket retention. Having a doc in place with the latter and any other important notes regarding how to configure this layer.

Use Case

Be able to define them so they can be loaded, parsed, and managed programmatically. An example of those rules would be this metrics