rpk: print license expiration warning

[r-vasquez]

Cover letter

Adding an alert in rpk for:

• License is about to expire when expires < 30 for --format text (default)

Adding an additional field to license info when the license is expired:

• license_expired for json format, License Expired for text.

rpk cluster license info --api-urls '0.0.0.0:9645' 
LICENSE INFORMATION
===================
Organization:      redpanda-testing
Type:              enterprise
Expires:           36479 days
Version:           0
License Expired:   true

rpk cluster license info --api-urls '0.0.0.0:9645' --format json
{
  "format_version": 0,
  "org": "redpanda-testing",
  "type": "enterprise",
  "expires": 36479,
  "license_expired": true
}

Release notes

• none

[twmb]

It's a bit odd to have these conditionals so far away from each other (one check for < 0 above, another check here). I think these should both be in one place above, or both be here (and don't emit any warning on expired for json, instead exit 1)

[r-vasquez]

I did it this way because I wanted to print a warning for "license expiring soon" only in --format plain. With your feedback I'll move this to:

1. If --format json exit 1 if the license is expired and NO warning text.
2. if --format plain exit 1 if the license is expired and print warning.
2a. if --format plain exit 0 and print a warning for "license expiring soon" check update below

[r-vasquez]

Update:

• Now adding a field "license_expired" for --format json when the license is expired.
• Adding field License Expired for --format plain when the license is expired.
• Removed warning in json format

[r-vasquez]

Debug-clang-amd64 ducktape failure: #4772