Expose direct TSDB querying in v2 API

[fabxc]

I would like the v2 API to expose a minimal layer to query the TSDB directly on top of the admin actions we expose. Any objections or concerns around this?

@brian-brazil @gouthamve

[brian-brazil]

Wouldn't that basically be the remote read endpoint?

[fabxc]

To a degree, sure. But I want to have it focused and extensible on TSDBs primitives, which are lower level than the remote-read path. I want to provide access to the on-disk/in-mem chunks as they are for example.
There's interesting tooling to be built on top of that but it might not be suitable for a simple gateway implementation.

[brian-brazil]

I'm not sure we should be offering that level of detail via the API that can be used by the average user, it sounds like something that belongs more in promtool.

[gouthamve]

Yep, but promtool would be needing the APIs. Also, given this is an admin API, I think it is fine.

[fabxc]

As it's get only, I wouldn't necessarily put it under admin/ – but would if not otherwise acceptable.
I wasn't looking at promtool use cases per se. The reason why this couldn't go into external tooling is because that doesn't give us access to in-memory blocks.