Add lifi intents endpoints to the docs

[MakMuftic]

Summary

Docs need to be updated to cover the new endpoints

Acceptance Criteria

• Replace the direct use of liquidity API for users with using lifi-intents/rfq endpoint
• Introduce new section in API reference that merges current 'Swaps' and the new LiFI Intents calls under 'Solve RFQ' Needs to explain when to use which (Using Sprinter Liquidity --> LiFi Intents and as fallback/ legacy also list Swap API that uses public onchain liquidity)
• Check and fix all examples building on those0, e.g. asset issuer and redemption liquidity flows

QA Details