Clean up old outdated tutorial and notebooks content

[robbibt]

The Open Data Cube website and organisation contains numerous old tutorial content that is no longer maintained, or updated to follow best-practice odc-stac and odc-geo approaches. Now that we have an official tutorials repo (https://github.com/opendatacube/tutorials), we should consider archiving or removing some of the older content below:

• Data Cube Applications Library (https://www.opendatacube.org/dcal)
• https://github.com/opendatacube/datacube-notebooks
• https://github.com/opendatacube/de_hackathon_2024
• https://github.com/opendatacube/datacube-stac-example
• https://github.com/opendatacube/datacube-conference-2021
• https://github.com/opendatacube/datacube-conference-2020
• https://github.com/opendatacube/testbeds

This newer repo could also potentially belong in the new tutorials repo too:
https://github.com/opendatacube/tutorial-odc-product