Update metadata records format

[wtgee]

• Store one top-level document called metadata for each unit, with the specific sub-collection stored as a key name.
• Also create a document in the records collection for just the collection.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 70.40%. Comparing base (c0e6750) to head (e2f5748).

Files	Patch %	Lines
src/panoptes/pocs/utils/cli/network.py	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1269 +/- ## =========================================== + Coverage 70.39% 70.40% +0.01% =========================================== Files 100 100 Lines 8423 8423 Branches 1170 1170 =========================================== + Hits 5929 5930 +1 Misses 2343 2343 + Partials 151 150 -1 ```

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