Add --file option to task and query commands

[noramullen1]

Closes #915

[sanderson]

• Flags should be listed in alphabetical order, so each -f row should come before the -h row.

• Need to update the usage examples to not use the @ symbol.

  - influx query [query literal or @/path/to/query.flux] [flags]
  + influx query [query literal] [flags]

  - influx task create [query literal or @/path/to/query.flux] [flags]
  + influx task create [query literal] [flags]

• Need to update the examples on the following pages to not use the -f flag instead of @:

  • https://v2.docs.influxdata.com/v2.0/query-data/execute-queries/#influx-query-command
  • https://v2.docs.influxdata.com/v2.0/process-data/manage-tasks/create-task/#create-a-task-using-the-influx-cli
  • https://v2.docs.influxdata.com/v2.0/process-data/manage-tasks/update-task/#update-a-task-with-the-influx-cli

[sanderson]

One minor change and it's gtg.