[8.x] [Simulated function calling] specify that only one tool call can be performed at a time (#193556)

[kibanamachine]

Backport

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

• [Simulated function calling] specify that only one tool call can be performed at a time (#193556)

Questions ?

Please refer to the Backport tool documentation

[elasticmachine]

Pinging @elastic/obs-ai-assistant (Team:Obs AI Assistant)

[kibana-ci]

:yellow_heart: Build succeeded, but was flaky

• Buildkite Build
• Commit: a17d6dfbc178d67f91781a7d48058f8e1fe7fd9a

Failed CI Steps

• SLO Plugin @elastic/synthetics Tests

Metrics [docs]

✅ unchanged

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

cc @pgayvallet