Make file system metadata values strings

[rdner]

To better align with ECS and better store the values in Elasticsearch.

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.

How to test this PR locally

See steps in #36065

Related issues

• Closes [Filebeat] filestream input : Change file system information fields to string #36695
• Relates Undefined log.file.* fields breaking tests for filestream inputs integrations#7716

[bhapas]

Possible to backport this to 8.10 ?

[elasticmachine]

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• Start Time: 2023-09-28T08:52:45.079+0000

• Duration: 71 min 52 sec

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Test	Results
Failed	0
Passed	28350
Skipped	2013
Total	30363

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[rdner]

@jlind23 it's technically a breaking change, do you think we can backport it to 8.10 anyway? It would fix some things for integration developers.

[jlind23]

@rdner No we shouldn't backport any breaking change in a patch release. 8.11 is lined up to be out soon so better stick with 8.11. Moreover if it's a breaking change, we need to have a proper entry in the release note for this.

[ycombinator]

LGTM.