[receiver/loadgen] Add optional performance optimization to reuse pdata struct

[carsonip]

Add a configurable performance optimization to reuse pdata struct.

goos: linux
goarch: amd64
pkg: github.com/elastic/opentelemetry-collector-components/receiver/loadgenreceiver
cpu: 11th Gen Intel(R) Core(TM) i7-11800H @ 2.30GHz
BenchmarkLogsGenerator/perfReusePdata=false-16              1377            798174 ns/op          541745 B/op       6447 allocs/op
BenchmarkLogsGenerator/perfReusePdata=true-16               6182            199226 ns/op             777 B/op         36 allocs/op
BenchmarkMetricsGenerator/perfReusePdata=false-16            652           1741115 ns/op         1418367 B/op      17053 allocs/op
BenchmarkMetricsGenerator/perfReusePdata=true-16             734           1623597 ns/op         1268901 B/op      16199 allocs/op
BenchmarkTracesGenerator/perfReusePdata=false-16             164           7367952 ns/op         7378519 B/op      29728 allocs/op
BenchmarkTracesGenerator/perfReusePdata=true-16              409           2972062 ns/op           16738 B/op        335 allocs/op
PASS
ok      github.com/elastic/opentelemetry-collector-components/receiver/loadgenreceiver  9.582s
PASS
ok      github.com/elastic/opentelemetry-collector-components/receiver/loadgenreceiver/internal/list    0.047s
?       github.com/elastic/opentelemetry-collector-components/receiver/loadgenreceiver/internal/metadata        [no test files]