Add support for REST based remote functions

[Joe-Abraham]

Description

This issue proposes to add support for REST-based remote functions in Velox, following RFC-0007 from Presto. This will support dynamic registration and execution of remote functions, unifying the metadata and execution. This will enable Presto C++ deployments to define remote functions at runtime and improve integration between custom function servers and Presto.

Impact:

No impact on existing users or behaviour.

[Yuhta]

CC: @pedroerp @mbasmanova

[pedroerp]

Cc: @kunigami who has been working on remote functions as well.