Add support for typed internal pprof transfers

[aleks-p]

Currently, pprof data is being sent as raw bytes in responses from query backend nodes, to backend and frontend nodes.

This has the benefit of a tightly controlled serialization and potentially smaller payloads, however tests have shown that letting connectrpc handle serialization results in less overhead for large requests, when combined together with #4422. I am yet to confirm what exactly causes the improvement, my guess is that the manual compression is more resource intense compared to the one from connectrpc but I will try to capture a diff profile to fully understand this.

End-to-end benchmark, with individual profiles having ~100-500k samples, ~50-100k locations, ~10-20k unique strings.

goos: darwin
goarch: arm64
pkg: github.com/grafana/pyroscope/pkg/test/integration
cpu: Apple M2 Pro
                                │ flat-bytes.txt │           flat-typed.txt           │
                                │     sec/op     │   sec/op    vs base                │
_ReadPath/SelectMergeProfile-10       9.311 ± 2%   6.558 ± 1%  -29.57% (p=0.000 n=10)

                                │ flat-bytes.txt │            flat-typed.txt            │
                                │      B/op      │     B/op      vs base                │
_ReadPath/SelectMergeProfile-10     14.73Gi ± 2%   11.63Gi ± 1%  -21.05% (p=0.000 n=10)

                                │ flat-bytes.txt │           flat-typed.txt            │
                                │   allocs/op    │  allocs/op   vs base                │
_ReadPath/SelectMergeProfile-10      81.27M ± 2%   72.63M ± 0%  -10.63% (p=0.000 n=10)

TODO:

• stress test in internal environments
• capture a diff profile, to understand where the gains come from
• decide if we want this configured separately, or as part of Add ability to use flat query plan for pprof queries #4422

Note before merging:
Once #4422 is merged, we should adjust the new aggregator introduced there (pkg/frontend/readpath/queryfrontend/report_aggregator.go) to support typed responses.