datacube lacks pytest plugin packages for application built on odc integration testing

[pindge]

digitalearthau (https://github.com/GeoscienceAustralia/digitalearthau) github repo has a testing package that prepares an empty database for odc testing, digitalearthau split pathways with current datacube-core years ago, it originally was kept to enable testing exclusively digitalearthaustralia products, most of the repo's code are no longer maintained, but this testing package would be great assets to include in opendatacube/datacube-core

https://github.com/GeoscienceAustralia/digitalearthau/blob/071d3e649b2c074a660220bc03857af623d7855b/digitalearthau/testing/factories.py#L38-L61

https://github.com/GeoscienceAustralia/digitalearthau/blob/071d3e649b2c074a660220bc03857af623d7855b/digitalearthau/testing/factories.py#L64-L74

https://github.com/GeoscienceAustralia/digitalearthau/blob/071d3e649b2c074a660220bc03857af623d7855b/digitalearthau/testing/factories.py#L77-L100

this allows applications built on odc to init database, add metadata, add product and add datasets for integration testing, i.e.

https://github.com/opendatacube/datacube-explorer/blob/e8c1c268e4b4c9bb4d75ab9968a25e1b539f5761/integration_tests/conftest.py#L42-L106