Suppport for ingesting compressed files via influx write

[danxmoran]

Proposal:
Allow influx write to read compressed LP / CSV files from disk.

Current behavior:
influx write only supports reading uncompressed files.

Desired behavior:
Passing a gzip file to influx write Just Works. Some details:

• gzip is auto-detected for files with extension .gz
• Auto-detection runs before the CSV vs. LP detection, so .csv.gz should work
• A new flag can be used to force gzip or not

Use case:
Make it easier for customers to onboard large amounts of data at a time.