Add data key to breakdown documents if missing

[thalassemia]

When retrieving data from MongoDB, the assemble_data function expects each document to have a data key. When a document is too large, the breakdown_data method splits the large nested dictionary into smaller sub-dictionaries, some of which may not have a data key after the split. This PR ensures that all documents have a data key, not just those that also have a corresponding time key. This fixes an issue where a very large configuration document (no time key) is broken down into sub-dictionaries, one of which lacks the data key and breaks assemble_data.

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[eagmon]

Good find @thalassemia!

[eagmon]

@thalassemia do you need a new release?

[thalassemia]

Yeah a new release would be great! As an aside, I want to try creating GitHub Actions tests for the MongoDB functionality. I'll do some testing and hopefully have a PR up in the next week or so.

[eagmon]

Great idea to test mongoDB functionality. I'll merge and release this now, v1.6.2