[Feature] Cleanup OECD CLI Endpoint.

[deeleeramone]

1. Why?:

   • Improve function response and eliminate the use of local storage.
   • URL needed updating.
   • Multiple countries not allowed.

2. What?:

   • Multiple country is allowed.
   • Added missing country groups as choices.
   • Adds adjustment parameter, ["amplitude", "normalized"]
   • Adds growth_rate parameter, [True, False]

3. Impact:

   • Improved function response and usability.
   • Not a breaking change, only additive.

4. Testing Done:

   • Updated integration tests
   • Recaptured unit test cassettes.