Use sql unnest to optimize entity insertion

[ktuite]

Related to #1095

Happy to report that I was able to insert 500,000 entities w/ 10 properties in about ~30 seconds (on my M3 mac) with this sql.unnest change.

That payload was about 76,000KB (76MB) and this limit was increased to 250000kb (250MB)
service.use(bodyParser.json({ type: 'application/json', limit: '250kb' }));

What has been done to verify that this works as intended?

Tests of small insertions still work.
I tried it on my own with those larger numbers.

Why is this the best possible solution? Were any other approaches considered?

There is still more to do to create many entities at once (streaming JSON?), but I think it's worth merging this particular change now so the bottleneck is no longer the database insert.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

Before submitting this PR, please make sure you have:

• run make test and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced

[matthew-white]

Very exciting that the database is no longer the bottleneck! 🎉 I have a question about insertMany(), but this is looking like a nice change to me.