Add support for adding new fields to an iceberg table

[tomighita]

Is your feature request related to a problem or challenge?

Currently, the API doesn't allow users of the library to modify the tables' schemas. This makes it quite tricky to handle schema changes to the tables.

Describe the solution you'd like

Ideally, there should be a AddFieldsAction action which implements the TransactionAction trait, which exposes an interface through which one can add new fields to an iceberg table

Willingness to contribute

I can contribute to this feature independently