Adding custom variables for cloud study

[LisaBock]

Description

For a cloud study I would need some new custom variables which are

• cloud top pressure (ctp)
• cloud effective radius (reff)
• temperature at 1000 hPa (ta1000)
• vertical velocity at 700 hPa (wap700)

Closes #2481

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.70%. Comparing base (0a58be1) to head (0f6c30f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2482   +/-   ##
=======================================
  Coverage   94.70%   94.70%           
=======================================
  Files         249      249           
  Lines       14114    14114           
=======================================
  Hits        13367    13367           
  Misses        747      747           

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