Add ubiquiti Airfiber model support.

[cchance27]

Pre-Request Checklist

• Passes rubocop code analysis (try rubocop --auto-correct)
• Tests added or adapted (try rake test)
• Changes are reflected in the documentation
• User-visible changes appended to CHANGELOG.md

Description

This PR creates and adds support for backing up the latest config from the airfiber from telnet/ssh.

[codecov-io]

Codecov Report

Merging #1748 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1748   +/-   ##
=======================================
  Coverage   63.42%   63.42%           
=======================================
  Files          30       30           
  Lines        1490     1490           
=======================================
  Hits          945      945           
  Misses        545      545

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[wk]

Looks great and complete, thanks!