Cherry-pick #21214 to 7.x: [Filebeat][httpjson] Add recursive split to httpjson

[marc-gr]

Cherry-pick of PR #21214 to 7.x branch. Original message:

What does this PR do?

Adds ability to split recursively to have more than one level of split events by functionality.

NOTE: uses the .. notation instead of . to avoid breaking users using . notation currently.

Why is it important?

This will unblock the development of some modules.

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.

We do not want to add it to the changelog since is only for internal use and to be removed soon

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #21252 opened]

• Start Time: 2020-09-23T13:44:28.404+0000

• Duration: 72 min 40 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2501
Skipped	388
Total	2889