Search API: Update plan API to support query limit

[kangzj]

We want to keep the API as compatible as possible, because we'll have the same code consuming the API for old versions.

Suggested changes to the API:

• Add a flag to identify whether it's on our new pricing or not. e.g. "pricing": "2022"
• Add plan allowed maximum usage. e.g. current_plan: { max_records, max_search_requests, cost }
• Add how many records indexed and how many search requests made in the current billing cycle. e.g. records_indexed, search_requests_current_month
• Add the plan the site will be on the next month. e.g. plan_next_month: {max_records, max_search_requests, cost}
• Billing cycle from ... to ...
• Any other attributes required

P2: pbtFFM-21I-p2#comment-2747