add athenalib package to go-libraries

[leslie-corbalt]

https://jiraent.cms.gov/browse/CMCSMACD-6748

PR Description

add the athenalib package that is in the cost-analysis repo to corbaltcode/go-libraries.

Tested:
I verified that professor-mac successfully imported this package and passed all tests. I also deployed this branch to professor-mac-dev successfully.

PR Checklist

• New automated tests have been written to the extent possible.
• The code has been checked for structural/syntactic validity.
  • AMI/application: a build was performed
  • terraform changes: "terraform plan" checked on every affected environment
• (If applicable) the code has been manually tested on our infrastructure.
  • AMI/application: deployed an a test or dev environment
  • terraform changes: applied to test or dev environment
  • script: run against test or dev environment
• Likely failure points and new functionality have been identified and tested manually.
  Examples:
  • Application manually run in a way that triggers any new branches
  • AMI logged into and changes verified from login shell
• Pull request description includes a description of all the manual steps performed to accomplish the above.

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[ben-harvey]

LGTM!

[leslie-corbalt]

#26