Check that the Java / Scala package is installed when needed

[EnricoMi]

Provides a meaningful error message when user accesses a spark extension function in Python that requires the Java / Scala package:

RuntimeError: Java / Scala package not found! You need to add the Maven spark-extension package to your PySpark environment: https:/G-Research/spark-extension#python

Before, the error was:

TypeError: 'JavaPackage' object is not callable

Improves #242
Supersedes #244

[github-actions]

Test Results

   624 files   -  13     624 suites   - 13   1h 46m 42s ⏱️ + 1m 49s
   511 tests +  1     511 ✅ +  1    0 💤 ±0  0 ❌ ±0 
19 580 runs   - 413  19 016 ✅  - 419  564 💤 +6  0 ❌ ±0 

Results for commit 0eaaa7d. ± Comparison against base commit 3a046ca.

♻️ This comment has been updated with latest results.