out_lib: support config_map

[nokute78]

This patch is to support config_map for out_lib.

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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
• [X] Debug log output from testing the change

• [X] 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-out_lib 
==20167== Memcheck, a memory error detector
==20167== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==20167== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==20167== Command: bin/flb-rt-out_lib
==20167== 
Test metrics_msgpack...                         [ OK ]
Test metrics_json...                            [ OK ]
Test format_json...                             [ OK ]
Test format_msgpack...                          [ OK ]
Test max_records...                             [ OK ]
SUCCESS: All unit tests have passed.
==20167== 
==20167== HEAP SUMMARY:
==20167==     in use at exit: 0 bytes in 0 blocks
==20167==   total heap usage: 10,137 allocs, 10,137 frees, 5,152,601 bytes allocated
==20167== 
==20167== All heap blocks were freed -- no leaks are possible
==20167== 
==20167== For lists of detected and suppressed errors, rerun with: -s
==20167== 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.