Create vParquet5

[joe-elliott]

We have not yet begun on the next iteration of the vParquet format, but I would like to start collecting ideas for what we would include. The past two iterations have been focused on adding columns and features and so I propose we focus on removing columns and cleanup.

I would like to:

• Remove "well known" columns and rely instead on dedicated columns
  • This would remove a significant amount of complexity in our read/write paths as well reduce footer size
• Remove the ServiceStats columns in favor of a marshalled proto or json representation. We only return these on search and don't need them broken out into individual columns.
• Drop .list.element from repeated fields column names. We added this for compatibility with some ?? tooling, but we just broke compatibility with other tooling. Personally I'd prefer the simpler names.
• Dictionary-less dedicated columns as a place to put fields like json blobs and sql queries. Maybe split the 10 we have into 5 dict and 5 no dict?

Everything is up for discussion. Please put ideas here!

cc @stoewer, @mdisibio, @ndk