in_tcp: Add a capability to inject source IP

[cosmo0920]

Currently, in_tcp plugin does not offer adding source address feature.
This PR provides this feature.

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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

[INPUT]
    Name        tcp
    Listen      0.0.0.0
    Port        5170
    Chunk_Size  32
    Buffer_Size 64
    Format      json
    Source_Address_Key source_host

[OUTPUT]
    Name        stdout
    Match       *

• Debug log output from testing the change

Fluent Bit v2.1.7
* Copyright (C) 2015-2022 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/07/10 14:30:42] [ info] Configuration:
[2023/07/10 14:30:42] [ info]  flush time     | 1.000000 seconds
[2023/07/10 14:30:42] [ info]  grace          | 5 seconds
[2023/07/10 14:30:42] [ info]  daemon         | 0
[2023/07/10 14:30:42] [ info] ___________
[2023/07/10 14:30:42] [ info]  inputs:
[2023/07/10 14:30:42] [ info]      tcp
[2023/07/10 14:30:42] [ info] ___________
[2023/07/10 14:30:42] [ info]  filters:
[2023/07/10 14:30:42] [ info] ___________
[2023/07/10 14:30:42] [ info]  outputs:
[2023/07/10 14:30:42] [ info]      stdout.0
[2023/07/10 14:30:42] [ info] ___________
[2023/07/10 14:30:42] [ info]  collectors:
[2023/07/10 14:30:42] [ info] [fluent bit] version=2.1.7, commit=0714d10889, pid=372853
[2023/07/10 14:30:42] [debug] [engine] coroutine stack size: 24576 bytes (24.0K)
[2023/07/10 14:30:42] [ info] [storage] ver=1.1.6, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/07/10 14:30:42] [ info] [cmetrics] version=0.6.3
[2023/07/10 14:30:42] [ info] [ctraces ] version=0.3.1
[2023/07/10 14:30:42] [ info] [input:tcp:tcp.0] initializing
[2023/07/10 14:30:42] [ info] [input:tcp:tcp.0] storage_strategy='memory' (memory only)
[2023/07/10 14:30:42] [debug] [tcp:tcp.0] created event channels: read=21 write=22
[2023/07/10 14:30:42] [debug] [downstream] listening on 0.0.0.0:5170
[2023/07/10 14:30:42] [debug] [stdout:stdout.0] created event channels: read=24 write=25
[2023/07/10 14:30:42] [ info] [sp] stream processor started
[2023/07/10 14:30:42] [ info] [output:stdout:stdout.0] worker #0 started
[2023/07/10 14:30:44] [debug] [input chunk] update output instances with new chunk size diff=86, records=1, input=tcp.0
[2023/07/10 14:30:44] [debug] [task] created task=0x7f5a4802a4b0 id=0 OK
[2023/07/10 14:30:44] [debug] [output:stdout:stdout.0] task_id=0 assigned to thread #0
[0] tcp.0: [[1688967044.132801215, {}], {"key 1"=>123456789, "key 2"=>"abcdefg", "source_host"=>"tcp://127.0.0.1:46958"}]
[2023/07/10 14:30:44] [debug] [out flush] cb_destroy coro_id=0
[2023/07/10 14:30:44] [debug] [task] destroy task=0x7f5a4802a4b0 (task_id=0)
[2023/07/10 14:30:57] [debug] [input chunk] update output instances with new chunk size diff=95, records=1, input=tcp.0
[2023/07/10 14:30:58] [debug] [task] created task=0x7f5a4802bda0 id=0 OK
[2023/07/10 14:30:58] [debug] [output:stdout:stdout.0] task_id=0 assigned to thread #0
[0] tcp.0: [[1688967057.809867670, {}], {"msg"=>[{"key 1"=>123456789, "key 2"=>"abcdefg"}], "source_host"=>"tcp://127.0.0.1:35472"}]
[2023/07/10 14:30:58] [debug] [out flush] cb_destroy coro_id=1
[2023/07/10 14:30:58] [debug] [task] destroy task=0x7f5a4802bda0 (task_id=0)
^C[2023/07/10 14:30:59] [engine] caught signal (SIGINT)
[2023/07/10 14:30:59] [ warn] [engine] service will shutdown in max 5 seconds
[2023/07/10 14:31:00] [ info] [engine] service has stopped (0 pending tasks)
[2023/07/10 14:31:00] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2023/07/10 14:31:00] [ info] [output:stdout:stdout.0] thread worker #0 stopped

• Attached Valgrind output that shows no leaks or memory corruption was found

==373310== 
==373310== HEAP SUMMARY:
==373310==     in use at exit: 95,170 bytes in 702 blocks
==373310==   total heap usage: 2,921 allocs, 2,219 frees, 1,306,526 bytes allocated
==373310== 
==373310== LEAK SUMMARY:
==373310==    definitely lost: 0 bytes in 0 blocks
==373310==    indirectly lost: 0 bytes in 0 blocks
==373310==      possibly lost: 0 bytes in 0 blocks
==373310==    still reachable: 95,170 bytes in 702 blocks
==373310==         suppressed: 0 bytes in 0 blocks
==373310== Reachable blocks (those to which a pointer was found) are not shown.
==373310== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==373310== 
==373310== For lists of detected and suppressed errors, rerun with: -s
==373310== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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

fluent/fluent-bit-docs#1155

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.