go: plugin_proxy: Handle FLBPluginInit(cb_init) error correctly and plug a SEGV case

[cosmo0920]

As described in #8253, we should handle an error on initialization from Golang output plugin.
Currently, this should be discarded and not handled correctly. We should handle it properly.

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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

[SERVICE]
    Flush        5
    Daemon       Off
    Log_Level    info
    Plugins_File plugins.conf
    HTTP_Server  On
    HTTP_Listen  0.0.0.0
    HTTP_Port    2020
    storage.metrics On

[INPUT]
    Name gdummy
    Tag  dummy.local.ins1
    Dummy {"compact": true, "schema": 1, "message": "ok"}
    # threaded on

[OUTPUT]
    Name  gstdout
    Match *

[PLUGINS]
  Path /path/to/fluent-bit/build/in_gdummy.so
  Path /path/to/fluent-bit/build/out_gstdout.so

• Debug log output from testing the change
  If an error occurred on Golang plugin side, we can obtain the following log instead of SEGV:

% bin/fluent-bit -c fluent-bit.conf -Y -v -H -P 2020 -vv
* Copyright (C) 2015-2023 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/12/12 13:39:18] [ info] [fluent bit] version=2.2.1, commit=40978390b6, pid=2799088
[2023/12/12 13:39:18] [ info] [storage] ver=1.1.6, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/12/12 13:39:18] [ info] [cmetrics] version=0.6.5
[2023/12/12 13:39:18] [ info] [ctraces ] version=0.3.1
[2023/12/12 13:39:18] [ info] [input:gdummy:gdummy.0] initializing
[2023/12/12 13:39:18] [ info] [input:gdummy:gdummy.0] storage_strategy='memory' (memory only)
[2023/12/12 13:39:18] [ info] [gdummy] plugin initialized
[2023/12/12 13:39:18] [ info] [input:gdummy:gdummy.0] thread instance initialized
[flb-go] plugin parameter = ''
[2023/12/12 13:39:18] [error] [go proxy]: plugin 'gstdout' failed to initialize
[2023/12/12 13:39:18] [error] [output] could not initialize 'gstdout' plugin
[2023/12/12 13:39:18] [error] [output] failed to initialize 'gstdout' plugin
[2023/12/12 13:39:18] [error] [engine] output initialization failed
[2023/12/12 13:39:18] [error] [lib] backend failed
[2023/12/12 13:39:19] [error] [input:gdummy:gdummy.0] wrong event, type=2 op=1

[2023/12/12 13:39:19] [error] could not retrieve collectors signal from parent thread on 'gdummy.0'

• 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.

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

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

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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.

[ezdev128]

As described in #8253, we should handle an error on initialization from Golang output plugin. Currently, this should be discarded and not handled correctly. We should handle it properly.

Thanks a lot!