[onechat] Implement agent modes

[pgayvallet]

Summary

Follow-up of #223367
Fix https://github.com/elastic/search-team/issues/10259

This PR introduce the concept of agent mode, expose the research agent as a mode instead of a tool, and add the reason and plan modes.

Examples

Calling the Q/A (default) mode

POST kbn:/internal/onechat/chat
{
  "nextMessage": "Find all info related to our work from home policy"
}

Calling the researcher mode

POST kbn:/internal/onechat/chat
{
  "mode": "research",
  "nextMessage": "Find all info related to our work from home policy"
}

[pgayvallet]

/ci

[pgayvallet]

/ci

[pgayvallet]

/ci

[pgayvallet]

/ci

[pgayvallet]

/ci

[joemcelroy]

very nitty but was this suppose to be researchGoalToolName instead?

[pgayvallet]

Tool's name is set_research_goal, it's the "internal" tool exposed to the LLM in the first step to define the research goal based on the conversation. It's exposed as a tool because the LLM can also decide to answer with aplain text response if it thinks it need more info before starting the deep-research process

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 9c9db14

Failed CI Steps

• FTR Configs #5

Test Failures

• [job] [logs] FTR Configs #5 / Rule execution logic API - Basic License/Essentials Tier @ess @serverless @serverlessQA timestamp tests alerts generated from events with a timestamp in seconds is converted correctly into the forced ISO8601 format when copying KQL query should still use the @timestamp field even with an override field. It should never use the override field

Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
@kbn/onechat-common	136	144	+8
@kbn/onechat-server	92	90	-2
total			+6

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
@kbn/onechat-common	3	2	-1

Page load bundle

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

id	before	after	diff
onechat	10.9KB	10.9KB	+14.0B

Unknown metric groups

API count

id	before	after	diff
@kbn/onechat-common	203	214	+11
@kbn/onechat-server	177	179	+2
total			+13

History

• 💚 Build #311541 succeeded 8174399
• 💔 Build #311461 failed 9de2be1
• 💔 Build #311285 failed cb58073