[receiver/kafka] Pre-compute header attribute keys to avoid per-message string allocation

[paulojmdias]

Description

getMessageHeaderResourceAttributes concatenates "kafka.header." + headerName on every message for each configured extraction header. Since the header list comes from the config and never changes, we can build the mapping once at startup and just look up the pre-computed attribute key per message.

I did this before starting the execution of #46816 to avoid conflicts and mixing topics in the same PR.

The results are below, and I feel it deserves a review.

Testing

Added benchmark tests to measure the change.

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/receiver/kafkareceiver
cpu: Apple M3 Pro
                                                  │ header_attrs_main.txt │        header_attrs_fix.txt         │
                                                  │        sec/op         │   sec/op     vs base                │
GetMessageHeaderResourceAttributes/headers=1-12              46.24n ±  1%   55.35n ± 2%  +19.70% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=4-12              169.2n ± 22%   123.3n ± 1%  -27.15% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=8-12              340.6n ± 19%   221.0n ± 4%  -35.11% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=16-12             703.4n ±  1%   510.2n ± 3%  -27.48% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=32-12             1.838µ ±  2%   1.442µ ± 2%  -21.52% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=64-12             5.715µ ±  5%   4.930µ ± 4%  -13.72% (p=0.001 n=10)
GetMessageHeaderResourceAttributes/headers=128-12            15.71µ ± 11%   13.79µ ± 5%  -12.20% (p=0.000 n=10)
geomean                                                      845.6n         691.3n       -18.25%

                                                  │ header_attrs_main.txt │         header_attrs_fix.txt         │
                                                  │         B/op          │     B/op      vs base                │
GetMessageHeaderResourceAttributes/headers=1-12                56.00 ± 0%     32.00 ± 0%  -42.86% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=4-12               152.00 ± 0%     56.00 ± 0%  -63.16% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=8-12               280.00 ± 0%     88.00 ± 0%  -68.57% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=16-12               536.0 ± 0%     152.0 ± 0%  -71.64% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=32-12              1048.0 ± 0%     280.0 ± 0%  -73.28% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=64-12              2072.0 ± 0%     536.0 ± 0%  -74.13% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=128-12            4.242Ki ± 0%   1.224Ki ± 1%  -71.14% (p=0.000 n=10)
geomean                                                        531.9          172.3       -67.61%

                                                  │ header_attrs_main.txt │        header_attrs_fix.txt        │
                                                  │       allocs/op       │ allocs/op   vs base                │
GetMessageHeaderResourceAttributes/headers=1-12                3.000 ± 0%   2.000 ± 0%  -33.33% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=4-12                9.000 ± 0%   5.000 ± 0%  -44.44% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=8-12               17.000 ± 0%   9.000 ± 0%  -47.06% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=16-12               33.00 ± 0%   17.00 ± 0%  -48.48% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=32-12               65.00 ± 0%   33.00 ± 0%  -49.23% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=64-12              129.00 ± 0%   65.00 ± 0%  -49.61% (p=0.000 n=10)
GetMessageHeaderResourceAttributes/headers=128-12              257.0 ± 0%   129.0 ± 0%  -49.81% (p=0.000 n=10)
geomean                                                        31.77        17.08       -46.24%

[axw]

LGTM!