Refine _time_to_search_dims logic

[Ariana-B]

Reason for this pull request

Passing time as an int/float to dc.load was causing the query to return an unexpected date range due to the value being interpreted as seconds since epoch. Int/float is not documented as an accepted type for time in the first place and could be ambiguous.

Proposed changes

• Raise error if time is not provided as some form of datetime or a string
• Tweak and consolidate logic in _time_to_search_dims and _to_datetime

• Remove added millisecond in time range from like as it appears unnecessary

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

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📚 Documentation preview 📚: https://datacube-core--1561.org.readthedocs.build/en/1561/

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.78%. Comparing base (b6cebf5) to head (4bf8cb8).

:exclamation: Current head 4bf8cb8 differs from pull request most recent head 78948f5. Consider uploading reports for the commit 78948f5 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1561 +/- ## ======================================== Coverage 91.78% 91.78% ======================================== Files 132 132 Lines 14641 14621 -20 ======================================== - Hits 13438 13420 -18 + Misses 1203 1201 -2 ```

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