Rework Axiom Cloudwatch Forwarder

[dasfmi]

This PR revises the naming of CloudFormation stack elements to make their purpose clearer, and allows greater flexibility in filtering log groups that are applied as subscription filters to the (newly named) Lambda Forwarder, now using a combination of names, prefix and regular expression. It also introduces versioning to the CloudFormation stacks so breaking changes do not impact users, and introduces a new Unsubscriber stack for convenience.

TODO:

• Renames the Ingester to Forwarder, Backfiller to Subscriber and the LogsSubscriber to LogGroupsListener.
• Moves the stack templates to their own folder to improve readability with shorter file names
• Moves out the responsibility of creating log group subscription filters and gives it to the Subscriber component
• Subscriber component to handle different inputs for log groups selection (names list, prefix or regex pattern)
• Create Unsubscriber component
• Versioning the released stack templates
• Prefix the created log groups names with /aws/axiom to easily discard them from being forwarded

[dominicchapman]

Great job. LGTM 👍