[8.x] [inference] Add simulated function calling (#192544)

[kibanamachine]

Backport

This will backport the following commits from main to 8.x:

• [inference] Add simulated function calling (#192544)

Questions ?

Please refer to the Backport tool documentation

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 28e6057

Failed CI Steps

• SLO Plugin @elastic/synthetics Tests

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
observabilityAIAssistantApp	154.3KB	154.3KB	+64.0B

Public APIs missing exports

Total count of every type that is part of your API that should be exported but is not. This will cause broken links in the API documentation system. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats exports for more detailed information.

id	before	after	diff
inference	14	15	+1

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
inference	5.7KB	5.8KB	+92.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @pgayvallet