filter_expect: support 'result_key' property and add test code

[nokute78]

This patch is to

• Support result_key property and action result_key
• Add test code for filter_expect

A property action result_key will append a result that rule is matched or not.
It is useful to test to check if the result value is true or false.

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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:

• 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] Attached local packaging test output showing all targets (including any new ones) build.

Documentation

• [N/A] Documentation required for this feature

Backporting

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

Configuration

[INPUT]
    Name dummy

[FILTER]
    Name Expect
    Match *
    Action result_key
    result_key result_is
    Key_Not_Exists hoge

[OUTPUT]
    Name stdout
    Match *

Debug log / Valgrind output

The key result_is is added.

[1656831381.289275294, {"result_is"=>true, "message"=>"dummy"}]

$ valgrind --leak-check=full bin/fluent-bit -c expect.conf 
==98553== Memcheck, a memory error detector
==98553== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==98553== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==98553== Command: bin/fluent-bit -c expect.conf
==98553== 
Fluent Bit v1.9.6
* Copyright (C) 2015-2022 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/07/03 15:56:19] [ info] [fluent bit] version=1.9.6, commit=7b23b94676, pid=98553
[2022/07/03 15:56:19] [ info] [storage] version=1.2.0, type=memory-only, sync=normal, checksum=disabled, max_chunks_up=128
[2022/07/03 15:56:19] [ info] [cmetrics] version=0.3.5
[2022/07/03 15:56:19] [ info] [output:stdout:stdout.0] worker #0 started
[2022/07/03 15:56:19] [ info] [sp] stream processor started
[0] dummy.0: [1656831380.296893567, {"result_is"=>true, "message"=>"dummy"}]
^C[2022/07/03 15:56:22] [engine] caught signal (SIGINT)
[0] dummy.0: [1656831381.289275294, {"result_is"=>true, "message"=>"dummy"}]
[2022/07/03 15:56:22] [ warn] [engine] service will shutdown in max 5 seconds
[2022/07/03 15:56:22] [ info] [engine] service has stopped (0 pending tasks)
[2022/07/03 15:56:22] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2022/07/03 15:56:22] [ info] [output:stdout:stdout.0] thread worker #0 stopped
==98553== 
==98553== HEAP SUMMARY:
==98553==     in use at exit: 0 bytes in 0 blocks
==98553==   total heap usage: 1,233 allocs, 1,233 frees, 953,706 bytes allocated
==98553== 
==98553== All heap blocks were freed -- no leaks are possible
==98553== 
==98553== For lists of detected and suppressed errors, rerun with: -s
==98553== 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.

[nokute78]

Doc PR is fluent/fluent-bit-docs#836