Add replace_learner method

[basnijholt]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 38.46154% with 16 lines in your changes missing coverage. Please review.

Project coverage is 74.22%. Comparing base (97b20d8) to head (28d1c01).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
...tive_scheduler/_server_support/database_manager.py	38.46%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #241      +/-   ##
==========================================
- Coverage   74.72%   74.22%   -0.50%     
==========================================
  Files          22       22              
  Lines        2777     2890     +113     
==========================================
+ Hits         2075     2145      +70     
- Misses        702      745      +43     

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