Add per @elastic/elasticsearch peer dependency or specify which which ES version are supported

[mvehar]

[jacobwgillespie]

It's a good suggestion, the honest answer here is that there's not a specific supported version, it's roughly 7.x, but includes only what users have used / have submitted issues or PRs for. There's likely many small differences between the latest 7.15 and what's here...

I'm willing to merge any PRs for API changes that are compatible with the latest ES release, but no version is fully covered by the types at this point (when I initially implemented the types here, I think maybe 7.4 was the current version?).

As far as I know, the query builder portion of this module should be compatible with all ES versions, as it's very flexible, it's just the TypeScript types that might have missing pieces.