[Bug]: error messages and warnings should consistently go to stderr

[jschauma]

CLI Version

linode-cli v5.51.0 Built from spec version 4.176.0

Command

linode-cli linodes create [...args...] --json | jq -r .[].id

Output

parse error: Invalid numeric literal at line 1, column 6

Expected Behavior

12345678

Actual Behavior

The problem occurs because linode-cli prints warnings and error messages to stdout. In this case, the (successful) command prints

Using default values: {'authorized_users': ['jschauma']}; use the --no-defaults flag to disable defaults

to stdout before printing the json output. This then leads to tools not being able to consume the output as expected.

The correct behavior here is to send all error messages and warnings to stderr, like a good little Unix tool.

Steps to Reproduce

linode-cli linodes create [...args that produce a warning...] --json | jq -r .[].id

[ykim-akamai]

@jschauma Thank you for the contribution! Team will review the PR shortly 👍