[Enhancement] Multiple CFT Ingest for Rulegen

**Is your feature request related to a problem? Please describe.**
Not yet but it could become a problem.

A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
Rules are generated by ONE template and may not become custom for multiple when there are 100's or 1000's of Cloudformation Templates.

**Describe the solution you'd like**
The ability for cfn-guard rulegen to generate rules from more than one or many CloudFormation Templates and provide a Rule "Blessing" for IaC to roll out.

A clear and concise description of what you want to happen.
e.g.,: cfn-guard rulegen -t file1.yaml file2.yaml file3.yaml -o IaCBless.rules
e.g.,: cfn-guard rulegen -folder -t ~/.CFT/* -o IaCBless.rules

**Describe alternatives you've considered**

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**Additional context**
CFN-Guard would be an even greater tool for engineers if it learned from multiple CFT's what is ultimately allowed in an environment.

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Start at the cfn-guard rulegen command described in the issue and trace how a single -t template is currently handled. Define the supported multi-template or folder input and combined output behavior, then verify that rulegen accepts the examples and produces the requested rules.

Written by the indexing model from the issue text.