feat: DIA-1815: Add conditional dependencies in product tour

[niklub]

Ability to trigger product tours only if other product tours are completed using:

dependencies:
  - another_tour

steps:
  ...

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[codecov]

Codecov Report

Attention: Patch coverage is 43.75000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 76.90%. Comparing base (53bdbcd) to head (6221142).
Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
label_studio/users/product_tours/serializers.py	43.75%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6918      +/-   ##
===========================================
- Coverage    76.93%   76.90%   -0.04%     
===========================================
  Files          175      175              
  Lines        14139    14154      +15     
===========================================
+ Hits         10878    10885       +7     
- Misses        3261     3269       +8     

Flag	Coverage Δ
pytests	76.90% <43.75%> (-0.04%)	⬇️

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