[libbeat][decoder] - Adding generic decoding package to libbeat

[ShourieG]

Type of change

• Enhancement

What does this PR do?

Adds a generic decoder in libbeat

Why is it important?

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• [ ]

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[mergify]

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[elasticmachine]

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• Start Time: 2023-07-10T08:52:15.889+0000

• Duration: 62 min 3 sec

Test stats 🧪

Test	Results
Failed	0
Passed	8181
Skipped	377
Total	8558

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[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @ShourieG? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit