Update ECS in auditbeat sessionmd processor

[mjwolf]

Proposed commit message

The sessionmd processor requires some of the latest process field from ECS, that are not currently in libbeat. This adds the required ECS field assets to the processor.

Without these fields, some field types would be incorrect. For example, session_leader.start should be date, but were sent as keyword.

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

To verify this, build auditbeat, and run auditbeat export template and verify the template is correct. In particular, verify that process hassession_leader, entry_leader, and group_leader, and that start and end have type "date".

How to test this PR locally

Related issues

• Closes [Security-Linux Platform Integrations] Auditbeat missing Session View Process fields  #38955

[elasticmachine]

Pinging @elastic/sec-linux-platform (Team:Security-Linux Platform)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @mjwolf? 🙏.
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

[elasticmachine]

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• Start Time: 2024-04-17T23:26:02.103+0000

• Duration: 42 min 35 sec

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Test	Results
Failed	0
Passed	467
Skipped	60
Total	527

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[pkoutsovasilis]

LGTM