Add custom cw agent configuration parmater store input

[mjcmtb]

Corresponding Issue(s) or trello card(s):

https://github.com/rackspace-infrastructure-automation/aws-terraform-internal/issues/162

Summary of change(s):

Add variables to optionally provide an alternate parameter store item that stores that CloudWatch agent configuration.

Will the change trigger resource destruction or replacement? If yes, please provide justification:

No

Does this update/change involve issues with other external modules? If so, please describe the scenario.

This same change will be made to the ec2_asg module.

If input variables or output variables have changed or has been added, have you updated the README?

Yes

Do examples need to be updated based on changes?

Yes - Updated.

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[johnctitus]

Changes look good, although I would also recommend we add a count to the "aws_ssm_parameter" "cwagentparam" resource, and don't create it if we were passed a custom cw agent config.

[johnctitus]

Looks good after changes

[bohn002]

LGTM