The AWS CloudWatch input behaviour is not fully documented in the docs

[zmoog]

Given the available docs about the CloudWatch logs input for Beats and Integrations [^1]:

• https://www.elastic.co/guide/en/beats/filebeat/current/filebeat-input-aws-cloudwatch.html
• https://docs.elastic.co/integrations/aws/cloudwatch#logs-reference

It is challenging for users to know what are the valid combinations for the following configuration options:

• log_group_arn
• log_group_name
• log_group_name_prefix

We need to update existing docs to guide users in learning all the supported configurations and their tradeoffs.

[^1]: Please add more links if I need to include something!

[lucabelluccini]

Related https://github.com/elastic/integrations/issues/5224