Token usage dashboard

**What the feature is **
Monitor your LLM token usage with an out of the box dashboard.

Elastic now ships a built-in Inference Token Usage dashboard that lets you monitor the LLM token consumption driven by AI features: Agent Builder, the AI Assistant, and other inference-backed capabilities, directly inside Kibana. The dashboard is created automatically when you enable a single toggle in GenAI settings.

Start by locating Kibana's GenAI settings and the existing Inference Token Usage dashboard, then review how Agent Builder, the AI Assistant, and other inference-backed capabilities expose token consumption. Done means a single GenAI setting enables an automatically created dashboard that monitors this usage.

Written by the indexing model from the issue text.