Allow importing parquet files with arbitrary root column names.

[nicktobey]

Parquet represents schemas as trees with a root node, and columns as paths from the root to a leaf.

parquet-go, the library Dolt uses to export tables as parquet files, uses parquet_go_root as the default name of the root node, but other names are allowed.

Prior to this PR, Dolt was assuming that the parquet file always had a root node named parquet_go_root, and would fail if any other name was used. This PR changes the behavior to have Dolt read the name from the file instead.

I also added a test that imports a simple parquet file that was not created with parquet-go.

[coffeegoddd]

@nicktobey DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
87615ac	ok	5937457

version	total_tests
87615ac	5937457

correctness_percentage
100.0

[jennifersp]

LGTM! Thank you!