[exporter/splunkhec] Improve performance and reduce memory consumption

[dmitryax]

Several optimizations can be made on the Splunk HEC exporter to increase its performance and reduce its memory footprint. This issue is intended to keep track of all the optimizations applied to the exporter:

• [chore] [exporter/splunkhec] Remove redundant state data and allocation #21765
• [chore] [exporter/splunkhec] Don't create the buffer for disabled type #21772
• [chore] [exporter/splunkhec] Split the profiling data before processing #21909
• [chore] [exporter/splunkhec] Simplify the batching process #21969
• [chore] [exporter/splunkhec] Do not copy all the data in case of error #21978
• [chore] [exporter/splunkhec] Reuse jsoniter stream/buffer #22016
• [chore] [internal/splunk] Don't use pointer for Event.Time field value #22030
• [exporter/splunk_hec] Apply compression if it's enabled in the config #22969
• [chore] [exporter/splunk_hec] Remove redundant bufState struct #22986

[atoulme]

Performance before and after (comparing between the first PR and the 7th one) (note some benchmarks have changed):

Before:

goos: darwin
goarch: arm64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/splunkhecexporter
Benchmark_pushLogData_100_10_10_1024
Benchmark_pushLogData_100_10_10_1024-10     	     410	   2702689 ns/op	 2441942 B/op	   34326 allocs/op
Benchmark_pushLogData_10_100_100_1024
Benchmark_pushLogData_10_100_100_1024-10    	     409	   2672872 ns/op	 2443447 B/op	   34506 allocs/op
Benchmark_pushLogData_10_0_100_1024
Benchmark_pushLogData_10_0_100_1024-10      	     840	   1331842 ns/op	 1226277 B/op	   17175 allocs/op
Benchmark_pushLogData_10_100_0_1024
Benchmark_pushLogData_10_100_0_1024-10      	     836	   1336186 ns/op	 1231659 B/op	   17342 allocs/op
Benchmark_pushLogData_10_10_10_256
Benchmark_pushLogData_10_10_10_256-10       	    2034	    568102 ns/op	  557723 B/op	    7689 allocs/op
Benchmark_pushLogData_10_10_10_1024
Benchmark_pushLogData_10_10_10_1024-10      	    4033	    267946 ns/op	  252992 B/op	    3456 allocs/op
Benchmark_pushLogData_10_10_10_8K
Benchmark_pushLogData_10_10_10_8K-10        	    1746	    687386 ns/op	 1861394 B/op	    2683 allocs/op
Benchmark_pushLogData_10_10_10_1M
Benchmark_pushLogData_10_10_10_1M-10        	    1555	    988593 ns/op	 6039903 B/op	    2684 allocs/op
Benchmark_pushLogData_10_1_1_1024
Benchmark_pushLogData_10_1_1_1024-10        	   41257	     27364 ns/op	   36548 B/op	     351 allocs/op
BenchmarkPushLogRecords
BenchmarkPushLogRecords-10                  	  205251	      5427 ns/op	   31409 B/op	      13 allocs/op
PASS

After

pkg: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/splunkhecexporter
Benchmark_pushLogData_10_10_1024
Benchmark_pushLogData_10_10_1024-10    	   38847	     31386 ns/op	   25167 B/op	     383 allocs/op
Benchmark_pushLogData_10_10_8K
Benchmark_pushLogData_10_10_8K-10      	   13942	     87630 ns/op	   71106 B/op	    1076 allocs/op
Benchmark_pushLogData_10_10_2M
Benchmark_pushLogData_10_10_2M-10      	   13096	     90047 ns/op	   73338 B/op	    1109 allocs/op
Benchmark_pushLogData_10_200_2M
Benchmark_pushLogData_10_200_2M-10     	     631	   1917114 ns/op	 1460391 B/op	   22010 allocs/op
Benchmark_pushLogData_100_200_2M
Benchmark_pushLogData_100_200_2M-10    	      79	  12951741 ns/op	11175612 B/op	  168047 allocs/op
Benchmark_pushLogData_100_200_5M
Benchmark_pushLogData_100_200_5M-10    	      61	  16757523 ns/op	14699264 B/op	  220011 allocs/op
BenchmarkConsumeLogsRejected
BenchmarkConsumeLogsRejected-10        	    1274	    935309 ns/op	  731880 B/op	   11012 allocs/op
PASS