Issue 357302 reviewer changed email notification

What does this MR do and why?

Related to Update assignee changed email text to be more r... (#357302 - closed)

Updated email notification template for 357302 issue, made added and removed reviewers into separate line.

Include pluralization text for more than one reviewers added. Tested in unit test, not able to provide screenshot without premium license.

Please see below examples

0 to any number of reviewers or added to existing list::

{users} were added as reviewers. {user} was added as an reviewer.

Any users removed from reviewers:

{users} were removed from reviewers. {user} was removed from reviewer.

Any users were removed from reviewers and any other users added as reviewers:

{added users} were added as reviewers. {removed users} were removed from reviewers

{added user} was added as an reviewer. {removed user} was removed from reviewers.

Back to 0 reviewers:

All reviewers were removed

Screenshots or screen recordings

Add a reviewer and removed a reviewer

All Reviewers Removed

How to set up and validate locally

gdk start 
bundle exec rspec spec/helpers/emails_helper_spec.rb

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