Support Parquet as an output format in the `-r` option

[max-hoffman]

Two related features that would have been useful fixing a recent bug:

Specifying an --asof flag for exports:

> dolt export table --asof <revspec> mytable mytable.parquet

Supporting --format pq for the sql command:

> dolt sql -r pq -q "select * from mytable as of <root value>"

[timsehn]

For the first one, you can just checkout the branch. The second one would be nice.

[fulghum]

Parquet output support for dolt sql is included in https://github.com/dolthub/dolt/pull/6068

[timsehn]

Jason fixed this :-)