Adding OECD Endpoints (CPI + Share Price Index)

[jmaslek]

1. Why?:

   • Expand macroeconomic data and provider coverage.

• [x] CPI
• [x] Share Price Index

2. What?:

   • Added CPI from oecd which doesn't require an api key - but the input parameters are a bit more confusing. Nothing like 29 possible expenditures.
   • Edited the standard model
   • Expanded cpi -> consumer_price_index in files
   • Added share_price_index standard model and Economy route.

3. Impact :

   • I did change the standard model to be compatible between fred + oecd, but the default values should work.
   • New standard model and provider endpoint to maintain.

4. Testing Done:

   • Unit/Integration tests.
   • CLI
   • Various combinations of countries.