feat: Support for Map value data type

[nquinn408]

Is your feature request related to a problem? Please describe.
Want to support map typed feature value in offline and online feature store.

Describe the solution you'd like
Since dict can be mapped to map type, then could be supported through feast

Describe alternatives you've considered
We have tried to flatten map into new feature view but is wasteful for feature view with lots of map type features

[franciscojavierarceo]

@nquinn408 I see you have a fork with some of these already supported? I think we technically already support dictionary types but maybe it's not documented or maybe under only some conditions?