in_opentelemetry: fix memory leak

[nokute78]

This patch is to fix following valgrind error.
The resource should be freed by opentelemetry__proto__collector__logs__v1__export_logs_service_request__free_unpacked.

==149281== 
==149281== HEAP SUMMARY:
==149281==     in use at exit: 688 bytes in 21 blocks
==149281==   total heap usage: 1,611 allocs, 1,590 frees, 1,258,568 bytes allocated
==149281== 
==149281== 688 (40 direct, 648 indirect) bytes in 1 blocks are definitely lost in loss record 9 of 9
==149281==    at 0x4848899: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==149281==    by 0x9893BC: system_alloc (protobuf-c.c:154)
==149281==    by 0x98940C: do_alloc (protobuf-c.c:167)
==149281==    by 0x98E30C: protobuf_c_message_unpack (protobuf-c.c:3063)
==149281==    by 0x9926B3: opentelemetry__proto__collector__logs__v1__export_logs_service_request__unpack (logs_service.pb-c.c:43)
==149281==    by 0x4BF436: binary_payload_to_msgpack (opentelemetry_prot.c:410)
==149281==    by 0x4C1922: process_payload_logs (opentelemetry_prot.c:1339)
==149281==    by 0x4C2406: opentelemetry_prot_handle (opentelemetry_prot.c:1647)
==149281==    by 0x4B942E: opentelemetry_conn_event (http_conn.c:99)
==149281==    by 0x244C82: flb_engine_start (flb_engine.c:1009)
==149281==    by 0x1DE9F4: flb_lib_worker (flb_lib.c:638)
==149281==    by 0x4FF4AC2: start_thread (pthread_create.c:442)
==149281== 
==149281== LEAK SUMMARY:
==149281==    definitely lost: 40 bytes in 1 blocks
==149281==    indirectly lost: 648 bytes in 20 blocks
==149281==      possibly lost: 0 bytes in 0 blocks
==149281==    still reachable: 0 bytes in 0 blocks
==149281==         suppressed: 0 bytes in 0 blocks
==149281== 
==149281== For lists of detected and suppressed errors, rerun with: -s
==149281== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

---

Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Run local packaging test showing all targets (including any new ones) build.
• [N/A] Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• [N/A] Documentation required for this feature

Backporting

• [] Backport to latest stable release.

Configuration

[INPUT]
    Name opentelemetry
    Port 4318

[OUTPUT]
    Name stdout

Debug/Valgrind output

1. Run fluent-bit
2. Send logs using telemetrygen logs --otlp-http --otlp-insecure --telemetry-attributes "key=\"value\""

Note: I installed telemetrygen using following command.

go install github.com/open-telemetry/opentelemetry-collector-contrib/cmd/telemetrygen@latest

$ valgrind --leak-check=full bin/fluent-bit -c otel.cfg 
==146487== Memcheck, a memory error detector
==146487== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==146487== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==146487== Command: bin/fluent-bit -c otel.cfg
==146487== 
Fluent Bit v2.2.1
* Copyright (C) 2015-2023 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/12/17 11:51:01] [ info] [fluent bit] version=2.2.1, commit=2389f44ee4, pid=146487
[2023/12/17 11:51:02] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/12/17 11:51:02] [ info] [cmetrics] version=0.6.5
[2023/12/17 11:51:02] [ info] [ctraces ] version=0.3.1
[2023/12/17 11:51:02] [ info] [input:opentelemetry:opentelemetry.0] initializing
[2023/12/17 11:51:02] [ info] [input:opentelemetry:opentelemetry.0] storage_strategy='memory' (memory only)
[2023/12/17 11:51:02] [ info] [input:opentelemetry:opentelemetry.0] listening on 0.0.0.0:4318
[2023/12/17 11:51:02] [ info] [output:stdout:stdout.0] worker #0 started
[2023/12/17 11:51:02] [ info] [sp] stream processor started
[0] v1_logs: [[1702781469.874892154, {"app"=>"server", "value"=>"value"}], {"message"=>"the message"}]
^C[2023/12/17 11:51:11] [engine] caught signal (SIGINT)
[2023/12/17 11:51:11] [ warn] [engine] service will shutdown in max 5 seconds
[2023/12/17 11:51:12] [ info] [engine] service has stopped (0 pending tasks)
[2023/12/17 11:51:12] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2023/12/17 11:51:12] [ info] [output:stdout:stdout.0] thread worker #0 stopped
==146487== 
==146487== HEAP SUMMARY:
==146487==     in use at exit: 0 bytes in 0 blocks
==146487==   total heap usage: 1,630 allocs, 1,630 frees, 1,414,216 bytes allocated
==146487== 
==146487== All heap blocks were freed -- no leaks are possible
==146487== 
==146487== For lists of detected and suppressed errors, rerun with: -s
==146487== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[edsiper]

thanks @nokute78

please adjust the commit prefix to in_opentelemetry: ...

[nokute78]

@edsiper I fixed commit message.

[edsiper]

thank you