Add new 3D blob tracking example

[Sven-248]

This PR introduces a new example showcasing 3D blob tracking (#478). In addition, the following updates have been made:

• New example added: A new example for generating and tracking 3D blobs has been added to the example folder

• Environment update: The environment-examples.yml file has been updated to include any necessary dependencies related to the new example

• Test function: A new test function has been added to tobac/testing.py to create a 3D blob

• Doc: The new 3d example has been added to the gallery with an appropriate thumbnail

• Have you followed our guidelines in CONTRIBUTING.md?

• Have you self-reviewed your code and corrected any misspellings?

• Have you written documentation that is easy to understand?

• Have you written descriptive commit messages?

• Have you added NumPy docstrings for newly added functions?

• Have you formatted your code using black?

• If you have introduced a new functionality, have you added adequate unit tests?

• Have all tests passed in your local clone?

• If you have introduced a new functionality, have you added an example notebook?

• Have you kept your pull request small and limited so that it is easy to review?

• Have the newest changes from this branch been merged?

[github-actions]

Linting results by Pylint:

Your code has been rated at 8.31/10 (previous run: 8.31/10, +0.00)
_{The linting score is an indicator that reflects how well your code version follows Pylint’s coding standards and quality metrics with respect to the RC_v1.6.x branch.
A decrease usually indicates your new code does not fully meet style guidelines or has potential errors.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.98%. Comparing base (9da0f65) to head (3ab7844).

Additional details and impacted files

@@              Coverage Diff              @@
##           RC_v1.6.x     #500      +/-   ##
=============================================
+ Coverage      63.55%   63.98%   +0.43%     
=============================================
  Files             27       27              
  Lines           3844     3890      +46     
=============================================
+ Hits            2443     2489      +46     
  Misses          1401     1401              

Flag	Coverage Δ
unittests	63.98% <100.00%> (+0.43%)	⬆️

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[Sven-248]

I recommend handling issue #37 (Calculation of velocity components-vectors) in a separate PR, as it seems to affect multiple example scripts beyond the one modified here.