Validate email addresses before saving them to the database

[Turbo87]

#921 introduced a way for users to change their registered email addresses, but the code in the PR did not check if the supplied email addresses are valid and only relied on the email verification process. This led us to having about two dozens "email addresses" in our database now that aren't actually valid email addresses (e.g. people replacing @ with [at] and other fun examples).

This PR passes the supplied email address to a .parse::<lettre::Address>() call and returns an HTTP error if the supplied email is invalid.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.20%. Comparing base (e8ee8c4) to head (a3b58d9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9365      +/-   ##
==========================================
- Coverage   89.20%   89.20%   -0.01%     
==========================================
  Files         283      283              
  Lines       29096    29107      +11     
==========================================
+ Hits        25956    25965       +9     
- Misses       3140     3142       +2     

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