Loki: Apply the ingester ring config to all other rings (distributor, ruler, query-scheduler)

[slim-bean]

What this PR does / why we need it:

Problem: Loki fails to start when using the default config (specifically any config which doesn't properly set the query-scheduler ring config)

Conceptually it makes sense to me to apply the ring config used in the ingesters to any other rings used by Loki. The likelyhood of someone using multiple ring stores between different components is extremly low.

It seems resonable then to use the ingester ring config for all rings.

Unfortunately the implementation of this is a fairly brittle mapping exercise because each ring uses a different struct for config (even though they are mostly similar and largely the same)

I know this being broken is blocking several things/people so this is my suggested fix.

I have an idea for a test, although it's crude but I don't have any better ideas:

msgf := "%s has changed, this is a crude attempt to catch mapping errors missed in config_wrapper.applyIngesterRingConfig when a ring config changes. Please add a new mapping and update the expected value in this test."

assert.Equal(t, 8,  reflect.TypeOf(distributor.RingConfig{}).NumField(), fmt.Sprintf(msgf, reflect.TypeOf(distributor.RingConfig{}).String()))
// Do this for all the other rings

seems better than nothing....

We can merge this PR as is and I'll follow up with the test, I know we are blocked a few places on this so we can merge this first else I'll push more to it tomorrow.

Which issue(s) this PR fixes:
Fixes #4533

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[dannykopping]

Thanks for this, @slim-bean!
It seems to me that we need to move the ring config to its own central definition and reuse it everywhere; I agree with you that using different ring configs is pretty unlikely.

[MichelHollands]

LGTM