feat(#190): version 2: add multi-db, batching and tags

[witash]

This is ready for review
It wasn't really possible to separate the issues included, so I added one big PR instead of several small ones.

It contains

• adding source to couchdb (this is a breaking change for cht-sync)
• adding dbname and instance, relying on source to document_metadata for mulit-db and multi-
• adds tags to base and telemetry models to allow users to separate the runs for base models and telemetry models if they want.
• adds batch_incremental macro to allow for small batches for document_metadata

[mrjones-plip]

I haven't spent enough time with the code prior to v1 to be confident in doing an in depth code review. I'll defer to @jkuester for any deep code dives!

I'll be sure to do a fair amount of black box testing in the docs PR I'm working and suggest we wait to have both PRs approved before merging. For example, there's no upgrade path documented and I'm not sure if this will impose additional changes on this v2 PR

otherwise approving to unblock!

[jkuester]

Very nice! Just one big question about our batching logic. At the end of the day duping less than 1000 rows in a 100_000 row batch is probably not too big of a deal, but maybe we can avoid it....

[medic-ci]

🎉 This PR is included in version 2.0.0 🎉

The release is available on GitHub release

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