Allow fresher Guzzle versions (7.0 and above) in composer dependencies

[MurzNN]

Many other modules needs the Guzzle version 7.0 or above, but in Drupal Console Core package it is locked to 6.x version:

        "guzzlehttp/guzzle": "~6.1"

Is there some important reasons for that lock, or we can simply allow installing fresher version of guzzle without any problems?

[MurzNN]

Found Drupal issue about this: https://www.drupal.org/project/drupal/issues/3104353
and https://www.drupal.org/project/drupal/issues/3220220