[FEATURE] Possibility to specify secondary index for `Symbol`

[enricobenedos]

We started using QuestDb in our production environment to store also historical EOD market data. About that we are experiencing slow queries when asking for "the first available data for that symbol":

SELECT * FROM eod_1d_raw 
WHERE identifier = 'BBG000BDTBL9'
LIMIT 0,1

so we tried to add the index for symbol column and now we are performing some tests (even if it seems that it doesn't solve the performance problem).

Shortly we recreate the eod_1d_raw table every day and now we need to create the associated index also.

Can you please add a way to specify we want the symbol index on table creation extension methods chain?