Column wise tooltip for table

#### Is your feature request related to a problem? Please describe

Need to give a description about the values in a particular column when hover on top of the column name.

#### Describe the solution you'd like

I would like to have a feature to show a tooltip for each column name instead of having a single tooltip for the entire table.
Something like shown below,

#### Describe alternatives you've considered

Tried to use the tooltip which already has for the entire table to convey the message. But that is not efficient when it come to the application.

#### Additional context

Discussion https://github.com/h2oai/wave/discussions/1784

Start by reading Discussion 1784 and locating the existing table-wide tooltip implementation. Determine how column headers are rendered and define completion as showing the appropriate column description when hovering each column name without relying on the table-wide tooltip.

Written by the indexing model from the issue text.