[ENH] owkaplanmeier: stricter DomainModel options

[JakaKokosar]

Issue

Time and Event variable selection have options that do not make sense.

Description of changes

Filter data domain before setting it as a DomainModel for time_var and event_var dropdown menu. TimeVariables and DiscreteVariables with values > 2 are excluded.

Includes

• [X] Code changes
• [ ] Tests
• [ ] Documentation

[codecov-io]

Codecov Report

Merging #8 (e2324a5) into master (1fe2cd3) will increase coverage by 0.08%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   93.73%   93.82%   +0.08%     
==========================================
  Files           2        2              
  Lines         351      356       +5     
==========================================
+ Hits          329      334       +5     
  Misses         22       22              

Impacted Files	Coverage Δ
...contrib/survival_analysis/widgets/owkaplanmeier.py	93.75% <100.00%> (+0.09%)	:arrow_up:

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