Add completion for 'conditionRef' field

[evidolob]

Fix: #244

Demo:

[codecov-commenter]

Codecov Report

Merging #337 into master will decrease coverage by 0.00%.
The diff coverage is 78.26%.

@@            Coverage Diff             @@
##           master     #337      +/-   ##
==========================================
- Coverage   73.87%   73.87%   -0.01%     
==========================================
  Files          46       47       +1     
  Lines        3415     3433      +18     
  Branches      635      637       +2     
==========================================
+ Hits         2523     2536      +13     
- Misses        892      897       +5     

Impacted Files	Coverage Δ
src/yaml-support/tkn-yaml-scheme-generator.ts	31.70% <44.44%> (-0.65%)	⬇️
src/yaml-support/tkn-conditions-provider.ts	100.00% <100.00%> (ø)
src/yaml-support/tkn-tasks-provider.ts	100.00% <100.00%> (ø)

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