Add conditional read-after–write support to rules evaluation

[pracucci]

What this PR does

This PR introduces conditional read-after-write (or strong read consistency) support for rule evaluations. This PR is based on grafana/mimir-prometheus#587.

How it works:

• The Prometheus ruler evaluates whether each rule in a group is independent or not. A rule is independent if no other rule depends on it and it doesn't depend on any other in the group.
• The information whether a rule is independent or not is stored in the RuleDetail inside the context passed down to the ruler's query function.
• Mimir uses a custom query function. In this PR I've introduced a query function wrapper which reads the RuleDetail from the context and inject Mimir-specific read consistency requirement in the context.
• The Mimir-specific read consistency requirement is passed, via context and HTTP header (remote querier), through the network so that it gets correctly enforced in the ingesters.

code easier in Prometheus

I will try to upstream the mimir-prometheus changes to Prometheus, in coordination with Danny's PR from which I've tool the dependency analysis code. However, I will not block on it.

Which issue(s) this PR fixes or relates to

N/A

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.

[dimitarvdimitrov]

nicely done, i really don't have any comments.

Would be nice if we can eventually improve rule.Independant to only apply where we need it (today it might significantly increase the number of read-after-write queries without needing that), but i suppose that's future work?

[pracucci]

Would be nice if we can eventually improve rule.Independant to only apply where we need it (today it might significantly increase the number of read-after-write queries without needing that), but i suppose that's future work?

Yes, it's on my plate but I wanted to keep the scope of mimir-prometheus PR smaller.

[pracucci]

@dimitarvdimitrov I've swapped the mimir-prometheus implementation with a simpler one (here) which doesn't include the concurrent rules evaluation support (given we don't need it in this PR). In the new mimir-prometheus implementation I've also exposed both "dependent rules" and "dependency rules" info, so in Mimir we can only enforce strong consistency on rules with dependencies.

I haven't update this PR description yet. Can you review the changes (this commit) first, please?

[dimitarvdimitrov]

I had a closer look at the second revision and still LGTM