fix: limit email subject length

[dyudyunov]

Description

Add limitation for subject length (128 chars) and the
corresponding help text.

Notes

This is a backport from the master branch: #154

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (open-release/quince.master@39c18ac). Click here to learn what that means.

Additional details and impacted files

@@                      Coverage Diff                      @@
##             open-release/quince.master     #196   +/-   ##
=============================================================
  Coverage                              ?   83.23%           
=============================================================
  Files                                 ?       47           
  Lines                                 ?      692           
  Branches                              ?      135           
=============================================================
  Hits                                  ?      576           
  Misses                                ?      116           
  Partials                              ?        0           

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