Add context, telemetry, GPT token analysis and the logic to get access token of learn knowledge index service

[wangzelin007]

1. Add GPT token logs
2. Add the logic to get access token of learn knowledge index service
3. Add context and custom context, the context refers to the native context of the function app. the custom context is part of the context and is used to store information used by telemetry and log.
4. Add telemetry to record the duration of each request and GPT call, consumed GPT tokens, error logs, etc.