Make solar_date() timezone aware.

[SpacemanPaul]

Reason for this pull request

The datacube.api.query.solar_date() function takes a dataset object and calculates it's local solar date, based on center time and central longitude. However, it assumes that the dataset center_time is in UTC timezone. If the the center_time is in some other timezone, an incorrect date may be returned.

See also: https://github.com/opendatacube/datacube-ows/issues/979

Proposed changes

• Call .astimezone(utc) on the center time before doing solar date calculations.

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

---

:books: Documentation preview :books:: https://datacube-core--1521.org.readthedocs.build/en/1521/

[codecov[bot]]

Codecov Report

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

Comparison is base (9fb8c8c) 91.75% compared to head (e77ee0d) 91.79%. Report is 3 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 #1521 +/- ## =========================================== + Coverage 91.75% 91.79% +0.03% =========================================== Files 132 132 Lines 14552 14617 +65 =========================================== + Hits 13352 13417 +65 Misses 1200 1200 ```

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