HIVE-28377: Add support for hive.output.file.extension to HCatStorer

[VenkatSNarayanan]

What changes were proposed in this pull request?

HCatStorer now respects hive.file.output.extension for the output files it writes.

Why are the changes needed?

Brings HCatStorer's feature set more in line with Hive's.

Does this PR introduce any user-facing change?

Adds support for a property to HCatStorer that would previously have been ignored.

Is the change a dependency upgrade?

No

How was this patch tested?

TestHCatExtension was added.