[BugFix] - Fix lowercase symbols

[IgorWounds]

1. Why? (1-3 sentences or a bullet point list):

   • The field_validator from the standard model wasn't being picked up by the CBOEDerivatesFetcher which resulted in errors when the symbol was lowercase.

2. What? (1-3 sentences or a bullet point list):

   • Ensures all symbols passed to the CBOEDerivatesFetcher are uppercase.

3. Impact (1-2 sentences or a bullet point list):

   • N/A

4. Testing Done:

   • Ensured it works.

[deeleeramone]

This impacts all the other providers as well. Intrinio symbols are all case-sensitive.

Previously, upper() was done in the same place that enforced conversion of all "symbol" fields to a string from a list.

[hjoaquim]

The issue is gone.