filter_parser: add record accessor support in parser filter

[agup006]

This PR authored by OpenAI Codex Agent introduces the ability to use the record accessor syntax within the filter parser. The record accessor syntax allows users to select nested fields via a specific format

#10364
#10330

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Testing
Before we can approve your change; please submit the following in a comment:

Example configuration file

service:
  flush: 1
  log_level: info

pipeline:
  inputs:
    - name: dummy
      dummy: '{"message": "hi", "nested": {"key1":"bye"}}'

  filters:
    - name: parser
      match: "*"
      parser: try
      key_name: $nested['key1']

  outputs:
    - name: stdout
      match: "*"

parsers:
   - name: json
     format: json

   - name: try
     format: regex
     regex: ^(?<extracted>.*)$

• Attached Valgrind output that shows no leaks or memory corruption was found

SUCCESS: All unit tests have passed.
==93006==
==93006== HEAP SUMMARY:
==93006== in use at exit: 0 bytes in 0 blocks
==93006== total heap usage: 30,489 allocs, 30,489 frees, 14,191,579 bytes allocated
==93006==
==93006== All heap blocks were freed -- no leaks are possible
==93006==
==93006== For lists of detected and suppressed errors, rerun with: -s
==93006== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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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