Fix Doctrine deprecations

[kevinpapst]

Description

and add a migration template to never forget to switch the import again

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I verified that my code applies to the guidelines (composer code-check)
• I updated the documentation (see here)
• I agree that this code is used in Kimai (see license)

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (49e69d1) 88.20% compared to head (95310e2) 88.15%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4608      +/-   ##
============================================
- Coverage     88.20%   88.15%   -0.05%     
- Complexity     8801     8803       +2     
============================================
  Files           785      786       +1     
  Lines         29435    29450      +15     
============================================
  Hits          25962    25962              
- Misses         3473     3488      +15     

Files	Coverage Δ
src/Doctrine/DsnParserFactory.php	0.00% <0.00%> (ø)