GcomBNPS: allow any max length for username/password

[freddy36]

Pre-Request Checklist

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

Description

Allow any max length for username/password in GcomBNPS model (max length varies between software versions)

[codecov-io]

Codecov Report

Merging #2022 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2022   +/-   ##
=======================================
  Coverage   63.32%   63.32%           
=======================================
  Files          30       30           
  Lines        1497     1497           
=======================================
  Hits          948      948           
  Misses        549      549

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[wk]

Thanks for this! Pulling it in.