Define core features / compliance level

[asfimport]

Parquet format is getting more and more features while the different implementations cannot keep the pace and left behind with some features implemented and some are not. In many cases it is also not clear if the related feature is mature enough to be used widely or more an experimental one.
These are huge issues that makes hard ensure interoperability between the different implementations.

The following idea came up in a discussion. Create a now document in the parquet-format repository that lists the "core features". This document is versioned by the parquet-format releases. This way a certain version of "core features" defines a level of compatibility between the different implementations. This version number can be written to a new field (e.g. complianceLevel) in the footer. If an implementation writes a file with a version in the field it must implement all the related "core features" (read and write) and must not use any other features at write because it makes the data unreadable by another implementation if only the same level of "core features" are implemented.
For example if we have encoding A listed in the version 1 "core features" but encoding B is not then at "complianceLevel = 1" we can use encoding A but we cannot use encoding B because it would make the related data unreadable.

Reporter: Gabor Szadovszky / @gszadovszky
Assignee: Gabor Szadovszky / @gszadovszky

_{Note: This issue was originally created as PARQUET-1950. Please see the migration documentation for further details.}