kernel: add release function

[nokute78]

This patch is to add releasing function for flb_kernel.

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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:

• [N/A] 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

• [N/A] Backport to latest stable release.

Debug/Valgrind output

$ valgrind --leak-check=full bin/fluent-bit -i cpu -o stdout
==71676== Memcheck, a memory error detector
==71676== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==71676== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==71676== Command: bin/fluent-bit -i cpu -o stdout
==71676== 
Fluent Bit v2.1.10
* Copyright (C) 2015-2022 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/09/18 09:08:41] [ info] [fluent bit] version=2.1.10, commit=47b42dd4df, pid=71676
[2023/09/18 09:08:42] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/09/18 09:08:42] [ info] [cmetrics] version=0.6.3
[2023/09/18 09:08:42] [ info] [ctraces ] version=0.3.1
[2023/09/18 09:08:42] [ info] [input:cpu:cpu.0] initializing
[2023/09/18 09:08:42] [ info] [input:cpu:cpu.0] storage_strategy='memory' (memory only)
[2023/09/18 09:08:42] [ info] [output:stdout:stdout.0] worker #0 started
[2023/09/18 09:08:42] [ info] [sp] stream processor started
[0] cpu.0: [[1694995723.119274183, {}], {"cpu_p"=>24.000000, "user_p"=>22.000000, "system_p"=>2.000000, "cpu0.p_cpu"=>24.000000, "cpu0.p_user"=>22.000000, "cpu0.p_system"=>2.000000}]
^C[2023/09/18 09:08:44] [engine] caught signal (SIGINT)
[2023/09/18 09:08:44] [ warn] [engine] service will shutdown in max 5 seconds
[0] cpu.0: [[1694995724.129985281, {}], {"cpu_p"=>16.000000, "user_p"=>16.000000, "system_p"=>0.000000, "cpu0.p_cpu"=>16.000000, "cpu0.p_user"=>16.000000, "cpu0.p_system"=>0.000000}]
[2023/09/18 09:08:44] [ info] [input] pausing cpu.0
[2023/09/18 09:08:45] [ info] [engine] service has stopped (0 pending tasks)
[2023/09/18 09:08:45] [ info] [input] pausing cpu.0
[2023/09/18 09:08:45] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2023/09/18 09:08:45] [ info] [output:stdout:stdout.0] thread worker #0 stopped
==71676== 
==71676== HEAP SUMMARY:
==71676==     in use at exit: 0 bytes in 0 blocks
==71676==   total heap usage: 1,574 allocs, 1,574 frees, 969,267 bytes allocated
==71676== 
==71676== All heap blocks were freed -- no leaks are possible
==71676== 
==71676== For lists of detected and suppressed errors, rerun with: -s
==71676== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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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.