Add notebook for tracking coastal sediment using optical flow vectors

[robbibt]

Proposed changes

This PR adds a new notebook for tracking coastal sediment through time using optical flow vector computer vision techniques.

Includes a new xr_optical_flow function with tests.

Closes issues (optional)

• Closes Issue #000

Checklist

If this is a notebook, then have you:

• Checked the structure of the notebook follows our DEA-notebooks template
• Removed any unused Python packages from Load packages
• Removed any unused/empty code cells
• Removed any guidance cells (e.g. General advice)
• Ensured that all code cells follow the PEP8 standard for code. The jupyterlab_code_formatter tool can be used to format code cells to a consistent style: select each code cell, then click Edit and then one of the Apply X Formatter options (YAPF or Black are recommended).
• Included relevant tags in the final notebook cell (refer to the DEA Tags Index, and re-use tags if possible)
• Tested notebook on the DEA Sandbox
• Cleared all outputs, run notebook from start to finish, and save the notebook in the state where all cells have been sequentially evaluated
• If applicable, update the Notebook currently compatible with line below the notebook title to reflect the environments the notebook is compatible with
• Check for any spelling mistakes using the DEA Sandbox's built-in spellchecker (double click on markdown cells then right-click on pink highlighted words). For example:

[review-notebook-app]

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[cbur24]

Looks awesome @robbibt! The xr_optical_flow function makes a nice addition to dea-tools as well. I wonder if its worth highlighting in the JOSS paper?

All the markdown text and code looks good to me. I played around with the figures using different colormaps and experimented with adding a basemap to the final figure to give a bit of context....feel free to revert any of it if you think its not helping.

I've also removed the dask cluster as I don't think you were using it for the datacube load, and looks as though xr_optical_flow uses concurrent.futures.

One suggestion: is there any benefit in the Optical Flow Modelling section of the notebook in providing a bit of context on the method= and radius= parameters for xr_optical_flow? Is the radius measured in pixels? Why is the default 20?