[Feature] Add Fred Release Tables

[deeleeramone]

1. Why?:

   • This feature adds a function similar to obb.economy.fred_series, but for the economic release tables.
   • Generic endpoint that returns relational table data for a specific release and date(s).
   • This function also serves as a discovery mechanism for individual FRED Series IDs that would otherwise be difficult to curate.

2. What?:

   • New route: obb.economy.fred_release_table()
   • Required parameter is release_id.
     • Found via obb.economy.fred_search(), or from the FRED/Federal Reserve websites.
   • element_id is the specific table from the release.
     • When not supplied the top-level sections/tables are returned with IDs that can be used for drill-down.0
   • Release and Element IDs are entered as strings, despite being numeric.
   • Frequency selection is not possible via this method, however release tables are often structured where each frequency (annual, quarterly) and parameter (seasonally adjusted, etc.) are a separate table (element_id) within the release_id.
   • Each release is looked up by date, multiple dates are allowed. No date retrieves the latest observations.

3. Impact:

   • Standard model that will likely have no use for other providers.

   • Improves the self-directed access to the vast amounts of data available from FRED.

   • Functions that curate release tables can recycle the Fetcher for specific uses.

4. Testing Done:

   • Unit/Integration tests.
   • Variety of releases on different frequency schedules.
   • Multiple dates, single dates, no dates.