Add link timeout to confirmation and reset email templates.

[jwag956]

• confirmation_instructions, reset_instructions now include a message stating how long the link is valid
• reset_instructions - make the link part of the message to improve localization (this was missed when many of the other templates were changed)
• Add configuration variables to change the email template names for confirmation, reset, change_email (more to come later)
• Use template variable configs to improve testing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.66%. Comparing base (17b3c81) to head (3a425d2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1245   +/-   ##
=======================================
  Coverage   98.66%   98.66%           
=======================================
  Files          43       43           
  Lines        5383     5383           
=======================================
  Hits         5311     5311           
  Misses         72       72           

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