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

---

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.70%. Comparing base (0a58be1) to head (0f6c30f).
Report is 196 commits behind head on main.

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           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

In order to maintain a backlog of relevant pull requests, we automatically label them as stale after 180 days of inactivity.

If this pull request is still important to you, please comment below to remove the stale label. Otherwise, this pull request will be automatically closed in 60 days. If this pull request only suffers from a lack of reviewers, please tag the @ESMValGroup/technical-lead-development-team so they can help you find a suitable reviewer.