Support otlp metadata ingestion

[SungJin1212]

This PR adds ingestion OTLP metadata.

Which issue(s) this PR fixes:
Fixes #6247

Checklist

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

[yeya24]

Let's also update /~https://github.com/cortexproject/cortex/blob/master/integration/otlp_test.go ?

[yeya24]

It looks like query fuzz test becomes super flaky after the upgrade. Issue seems the same. value 0 and NaN. Something worth checking.

query_fuzz_test.go:557: case 90 results mismatch.
        instant: stdvar without () (
          quantile without (test_label) (
            time(),
            sgn(count_values without () ("value", {__name__="test_series_2"} @ start() offset -4s))
          )
        )
        res1: {k="0", value="29"} => 0 @[1740625800.253]
        res2: {k="0", value="29"} => NaN @[1740625800.253]
    query_fuzz_test.go:557: case 91 results mismatch.
        range query: stdvar without () (
          quantile without (test_label) (
            time(),
            sgn(count_values without () ("value", {__name__="test_series_2"} @ start() offset -4s))
          )
        )
        res1: {k="0", value="20"} =>
        0 @[1740624610.376]
        0 @[1740624640.376]
        0 @[1740624670.376]
        0 @[1740624700.376]
        0 @[1740624730.376]
        0 @[1740624760.376]
        0 @[1740624790.376]
        0 @[1740624820.376]
        0 @[1740624850.376]
        0 @[1740624880.376]
        0 @[1740624910.376]
        0 @[1740624940.376]
        0 @[1740624970.376]
        0 @[1740625000.376]
        0 @[1740625030.376]
        0 @[1740625060.376]
        0 @[1740625090.376]
        0 @[1740625120.376]
        0 @[1740625150.376]
        0 @[1740625180.376]
        0 @[1740625210.376]
        0 @[1740625240.376]
        0 @[1740625270.376]
        0 @[1740625300.376]
        0 @[1740625330.376]
        0 @[1740625360.376]
        0 @[1740625390.376]
        0 @[1740625420.376]
        0 @[1740625450.376]
        0 @[1740625480.376]
        0 @[1740625510.376]
        0 @[1740625540.376]
        0 @[1740625570.376]
        0 @[1740625600.376]
        0 @[1740625630.376]
        0 @[1740625660.376]
        0 @[1740625690.376]
        0 @[1740625720.376]
        0 @[1740625750.376]
        0 @[1740625780.376]
        res2: {k="0", value="20"} =>
        NaN @[1740624610.376]
        NaN @[1740624640.376]
        NaN @[1740624670.376]
        NaN @[1740624700.376]
        NaN @[1740624730.376]
        NaN @[1740624760.376]
        NaN @[1740624790.376]
        NaN @[1740624820.376]
        NaN @[1740624850.376]
        NaN @[1740624880.376]
        NaN @[1740624910.376]
        NaN @[1740624940.376]
        NaN @[1740624970.376]
        NaN @[1740625000.376]
        NaN @[1740625030.376]
        NaN @[1740625060.376]
        NaN @[1740625090.376]
        NaN @[1740625120.376]
        NaN @[1740625150.376]
        NaN @[1740625180.376]
        NaN @[1740625210.376]
        NaN @[1740625240.376]
        NaN @[1740625270.376]
        NaN @[1740625300.376]
        NaN @[1740625330.376]
        NaN @[1740625360.376]
        NaN @[1740625390.376]
        NaN @[1740625420.376]
        NaN @[1740625450.376]
        NaN @[1740625480.376]
        NaN @[1740625510.376]
        NaN @[1740625540.376]
        NaN @[1740625570.376]
        NaN @[1740625600.376]
        NaN @[1740625630.376]
        NaN @[1740625660.376]
        NaN @[1740625690.376]
        NaN @[1740625720.376]
        NaN @[1740625750.376]
        NaN @[1740625780.376]
    query_fuzz_test.go:565: 
        	Error Trace:	/home/runner/work/cortex/cortex/integration/query_fuzz_test.go:565
        	Error:      	finished query fuzzing tests
        	Test:       	TestExpandedPostingsCacheFuzz
        	Messages:   	2 test cases failed

[SungJin1212]

@yeya24
I add the metadata test to e2e as well.
For the fuzz test, let's take a look.

[yeya24]

Merging this PR first as the failure is unrelated

[yeya24]

Looks like the result mismatch comes from prometheus/prometheus#14941
The behavior of stdvar and stddev changes in this PR.
They don't handle NaN sample before but now it is checked here.

Since it is a legit behavior, I propose that for any fuzzy tests that we compare with old release of Cortex (v1.18.x, v1.19.x), let's don't enable stdvar and stddev aggregation or simply ignore test failures if promql query contains these functions