Closes https://github.com/elastic/obs-ai-assistant-team/issues/413

Summary

This PR handles APM error AI insights via Agent Builder. This is done by consuming the common AI_INSIGHT attachment and introducing an "error" attachment.

• Adds an API to pre-fetch the error data and generate an LLM response by calling the inference client.
• Once the summary is generated it showed inline on the page
• The user can click on "start conversation" which opens to the agent builder flyout to continue the conversation

UI for AI insights

This PR consumes the common UI component in the observability-agent-builder package.

Testing

Observability test clusters were used for testing.

Testing instructions

1. Connect to a Observability test cluster
2. In Kibana, go to "Observability" --> "Service Inventory"
3. Pick a service and visit the "Error" tab and select an error
4. Click on "What's this error"

Screen recording

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Unit or functional tests were updated or added to match the most common scenarios
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.