Document the Map function in the documentation #11435

Is your feature request related to a problem or challenge?

We implemented map and make_map functions in #1136. We're better to have the corresponding documentation for them.

Describe the solution you'd like

As @alamb mentioned in #11361 (review), we can follow the https://datafusion.apache.org/user-guide/sql/scalar_functions.html#struct-functions to do it.

Describe alternatives you've considered

No response

Additional context

No response