DRAFT: Add support for CfnGuard rules

[bmorrissirromb]

Issue #, if available:
Closes #356

Description of changes:
This is currently a DRAFT, with a LOT of placeholders for where the code still needs to be developed.

The general idea here is to support CfnGuard rules through the usual RDK mechanisms (eg. CFTs).

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[bmorrissirromb]

Next milestones/things to work on:

• rdk create should create two files, a .guard file with the contents of the rule_code.guard sample, and a parameters.json file.
• rdk create will need some parameter validation and maybe support for additional parameters (eg. debug logging)
• rdk deploy and deploy-organization will need a lot of work to take those parameters and pass them to the right CFT. It may make sense to split CfnGuard-related rules into their own helper deployer functions since the required parameters are so different.