query: prepare remoteEndpoints for remote engine pruning

[SuperPaintman]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

This PR updates query.remoteEndpoints.Engines() method to satisfy the updated RemoteEndpoints interface (thanos-io/promql-engine#680):

 type RemoteEndpoints interface {
-	Engines() []RemoteEngine
+	Engines(mint, maxt int64) []RemoteEngine
 }

Now RemoteEndpoints.Engines() accepts mint and maxt parameters (min and max timestamp that any selector in the query can read). We will use these parameters later to prune TSDBInfos in query.remoteEndpoints (more context here: #8597).

Note 1:

This PR doesn't change the actual remoteEndpoints implementation. It only updates the method signature.

The mint and maxt params are safe to ignore, promql-engine can handle "un-pruned" engines.

Note 2:

I've temporarily replaced github.com/thanos-io/promql-engine (in go.mod) with my fork. I'll remove it once thanos-io/promql-engine#680 is merged.

Verification

• Unit tests in Change RemoteEndpoints interface to support remote engines pruning promql-engine#680.
• We tested the same changes in an internal fork we run.

---

Issue: #8597

CC: @MichaHoffmann , @fpetkovski