Warn if non-eo3 dataset has eo3 metadata type

[Ariana-B]

Reason for this pull request

The sole criteria for a dataset being recognised as an eo3 dataset is the inclusion of the eo3 schema in the definition. If the dataset is not considered eo3 due to a missing schema but is otherwise treated as eo3 due to the product metadata type, it can cause seemingly mysterious errors down the line, as seen on slack.

Proposed changes

• When resolving a dataset in Doc2Dataset, alert users if there is a mismatch between is_doc_eo3 and the product metadata type

  • [ ] Closes #xxxx
  • [x] Tests added / passed
  • [x] Fully documented, including docs/about/whats_new.rst for all changes

---

📚 Documentation preview 📚: https://datacube-core--1523.org.readthedocs.build/en/1523/

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9fb8c8c) 91.75% compared to head (6e8fef0) 91.79%. Report is 4 commits behind head on develop.

Files	Patch %	Lines
datacube/index/memory/_datasets.py	80.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1523 +/- ## =========================================== + Coverage 91.75% 91.79% +0.04% =========================================== Files 132 132 Lines 14552 14624 +72 =========================================== + Hits 13352 13424 +72 Misses 1200 1200 ```

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