tests: runtime: filter_nest: add test case for add_prefix

[nokute78]

This patch is add test case add_prefix of filter_nest

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

• [N/A] Example configuration file for the change
• [N/A] 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/flb-rt-filter_nest 
==51977== Memcheck, a memory error detector
==51977== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==51977== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==51977== Command: bin/flb-rt-filter_nest
==51977== 


(snip)

Test add_prefix...                              [2024/01/14 08:21:38] [ info] [fluent bit] version=2.2.2, commit=78c8aa46f0, pid=51977
[2024/01/14 08:21:38] [debug] [engine] coroutine stack size: 24576 bytes (24.0K)
[2024/01/14 08:21:38] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2024/01/14 08:21:38] [ info] [cmetrics] version=0.6.6
[2024/01/14 08:21:38] [ info] [ctraces ] version=0.4.0
[2024/01/14 08:21:38] [ info] [input:lib:lib.0] initializing
[2024/01/14 08:21:38] [ info] [input:lib:lib.0] storage_strategy='memory' (memory only)
[2024/01/14 08:21:38] [debug] [lib:lib.0] created event channels: read=48 write=49
[2024/01/14 08:21:38] [debug] [lib:lib.0] created event channels: read=52 write=53
[2024/01/14 08:21:38] [ info] [sp] stream processor started
[2024/01/14 08:21:38] [debug] [filter:nest:nest.0] Lift : Outer map size is 1, will be 1, lifting 1 record(s)
[2024/01/14 08:21:38] [debug] [input chunk] update output instances with new chunk size diff=48, records=1, input=lib.0
[2024/01/14 08:21:39] [debug] [task] created task=0x5760e20 id=0 OK
[2024/01/14 08:21:39] [debug] [test_filter_nest] received message: [1448403340.000000,{"_nested_key.key":"value"}]
[2024/01/14 08:21:39] [debug] [out flush] cb_destroy coro_id=0
[2024/01/14 08:21:39] [debug] [task] destroy task=0x5760e20 (task_id=0)
[2024/01/14 08:21:39] [ warn] [engine] service will shutdown in max 1 seconds
[2024/01/14 08:21:40] [ info] [engine] service has stopped (0 pending tasks)
[ OK ]
SUCCESS: All unit tests have passed.
==51977== 
==51977== HEAP SUMMARY:
==51977==     in use at exit: 0 bytes in 0 blocks
==51977==   total heap usage: 6,387 allocs, 6,387 frees, 3,155,566 bytes allocated
==51977== 
==51977== All heap blocks were freed -- no leaks are possible
==51977== 
==51977== For lists of detected and suppressed errors, rerun with: -s
==51977== 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.