[feature] Permit multiple metrics to be fetched from multiple tickers as 1 library call

[hydrosquall]

Lineage

1. The library was specified that multiple tickers only support single metrics in the docstring but not in error messages, leading to a confusing error message in here.
2. The error message was clarified in [fix] Validate multi-ticker pandas arguments #263.
3. Getting multiple metrics back in 1 API call from multiple tickers was requested as a new feature here

In the meantime, users have 2 alternatives

• Use something like the code snippet proposed here
• Share a bit about how the data structure you'd expected for a multi-metric dataframe with multiple tickers might look like (would wide/long tables work for your usecase, or would you prefer a multi-indexed dataframe)?