Fix forgot password functionality

[MaHaWo]

• add forgot and reset password functionality
• add some backend tests
• add route in frontend
• add respective page implementation in frontend

fixes #199

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 109 lines in your changes missing coverage. Please review.

Project coverage is 1.47%. Comparing base (4cbc0c8) to head (0a2d3a1).

Files with missing lines	Patch %	Lines
...end/src/routes/resetPassword/[[code]]/+page.svelte	0.00%	85 Missing and 1 partial ⚠️
...ntend/src/lib/components/UserForgotPassword.svelte	0.00%	20 Missing and 1 partial ⚠️
frontend/src/lib/components/UserLogin.svelte	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #217      +/-   ##
========================================
- Coverage   1.52%   1.47%   -0.06%     
========================================
  Files         83      84       +1     
  Lines       2488    2581      +93     
  Branches      95      96       +1     
========================================
  Hits          38      38              
- Misses      2370    2462      +92     
- Partials      80      81       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[MaHaWo]

flaky statistics test is still in here. it is fixed in #214