[exporter/splunkhecexporter] Add `OtelAttrsToHec` struct and related config fields #78787

Job	Run time
govulncheck (receiver-0)	46s
setup-environment	49s
govulncheck (receiver-1)	47s
govulncheck (receiver-2)	47s
govulncheck (receiver-3)	47s
govulncheck (processor-0)	48s
govulncheck (processor-1)	49s
govulncheck (exporter-0)	48s
govulncheck (exporter-1)	48s
govulncheck (exporter-2)	47s
govulncheck (exporter-3)	48s
govulncheck (extension)	47s
govulncheck (connector)	47s
govulncheck (internal)	47s
govulncheck (pkg)	47s
govulncheck (cmd-0)	1s
govulncheck (cmd-1)	48s
build-examples	1s
check-codeowners	1s
check-collector-module-version	1s
checks	1s
correctness-metrics	1s
correctness-traces	1s
cross-compile	1s
integration-tests-matrix	1s
lint-matrix	1s
unittest-matrix	1s
lint	1s
integration-tests	1s
unittest	1s
publish-check	1s
publish-dev	1s
coverage	1s
publish-stable	1s
rotate-milestone	1s
	12m 59s

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