GovCloud Config rule fixes for FedRAMP Low Conformance Pack

[iteuscher]

Issue #421 Conformance Pack for FedRamp not deployable in GovCloud

Description of changes:
The FedRAMP Low conformance pack does not function in AWS Gov Cloud. Specifically the rules listed below are not in GovCloud or several other regions. I performed a full analysis of the non-GovCloud Config Rules and provided suggestions for how to update the rules. The full content of my analysis is available in this public spreadsheet: https://docs.google.com/spreadsheets/d/1eKZpe2EPA-8RQkG6bWViwLRrdDeS4yUpvtvUpu_4WEg/edit?usp=sharing

For an example see the documentation below on root-account-mfa-enabled https://docs.aws.amazon.com/config/latest/developerguide/root-account-mfa-enabled.html

AWS Region: All supported AWS regions except China (Beijing), Asia Pacific (Thailand), Middle East (UAE), Asia Pacific (Malaysia), AWS GovCloud (US-East), AWS GovCloud (US-West), Mexico (Central), Israel (Tel Aviv), Canada West (Calgary), China (Ningxia) Region

Config rules that need to be fixed	Suggested Change	Note
cloudtrail-enabled	cloud-trail-enabled	Add hypen (cloud-trail)
ec2-instance-managed-by-systems-manager	ec2-instance-managed-by-ssm	Acronym for SSM
ec2-instances-in-vpc	instances-in-vpc	Remove ec2
ecs-task-definition-memory-hard-limit	--	Consider creating custom rule
multi-region-cloudtrail-enabled	multi-region-cloud-trail-enabled	Add hypen (cloud-trail)
opensearch-in-vpc-only	--	elasticsearch-in-vpc-only already used
restricted-common-ports	nacl-no-unrestricted-ssh-rdp	Use similar rule
restricted-ssh	incoming-ssh-disabled	Use similar rule
root-account-hardware-mfa-enabled	--	No root account MFA checks in GovCloud
root-account-mfa-enabled	--	No root account MFA checks in GovCloud
waf-regional-webacl-not-empty	--	Consider creating custom rule

These changes have been made in this pull request and I confirmed that this version of the conformance pack successfully deploys in AWS GovCloud.

I confirm these files are made available under CC0 1.0 Universal (https://creativecommons.org/publicdomain/zero/1.0/legalcode)