in_http: support for msgpack .

[pwhelan]

Summary

This is a backport of #8499 to the v3.1 series.

Description

This patch adds support for msgpack payloads to the in_http plugin, which can be emitted by out_http and used to be the default format for it.

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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.

• 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.

[edsiper]

@pwhelan pls check on DCO and other CI issues

[pwhelan]

The DCO issues continue to be problems from previous commits:

• Commit sha: 129748f, Author: edsiper, Committer: Eduardo Silva; Expected "edsiper 369718+edsiper@users.noreply.github.com", but got "github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
• Commit sha: 507d975, Author: Leonardo Alminana, Committer: Leonardo Alminana; The sign-off is missing.
• Commit sha: 7f20490, Author: leonardo-albertovich, Committer: GitHub; Expected "leonardo-albertovich leonardo.alminana@chronosphere.io", but got "Leonardo Alminana leonardo.alminana@chronosphere.io

To fix them would require me to rewrite the git history.

[edsiper]

while this looks like a good PR, 3.1 is pretty much getting small fixes for long-term stabilization. Since the functionality is already in GIT master (next v3.2) I will proceed to close the PR.