Index level ep13

[SpacemanPaul]

Reason for this pull request

Changes to the Index and IndexDriver APIs, as proposed in EP13.

Proposed changes

• New index_class method on IndexDriver
• connect_to_index() function is now implemented in the base class (calls from_config on the class returned by index_class)
• metadata_type_from_doc() method on IndexDriver deprecated in favour of index.metadata_type.from_doc()

• "supports" flags on Index: New flags, as per EP13, and make all flags default to False, so drivers have to explicitly declare all the flags they DO support.

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

[codecov[bot]]

Codecov Report

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

Comparison is base (9fbc596) 85.28% compared to head (82b0113) 85.33%.

Files	Patch %	Lines
datacube/index/abstract.py	94.73%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop-1.9 #1534 +/- ## =============================================== + Coverage 85.28% 85.33% +0.04% =============================================== Files 139 140 +1 Lines 14971 15018 +47 =============================================== + Hits 12768 12815 +47 Misses 2203 2203 ```

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