[BugFix] Fix metadata creation

[hjoaquim]

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

   • Metadata in a wrong format (namely json string) causes a poor UX.

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

   • Fixed iteration on the arguments so that the length of each argument is properly accessed.

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

   • No impact (metadata is optional).

4. Testing Done:

   • Running any endpoint with several arguments (before and after):

from openbb import obb
res = obb.equity.price.historical("AAPL,MSFT", provider="fmp", start_date="2022-01-01")
res.extra["metadata"]

5. Reviewer Notes (optional):

   • NA

6. Any other information (optional)

Before:

After: