Fix getTokenAccountsByOwner documentation: clarify required parameters

[TanmayDhobale]

Problem

The documentation for the getTokenAccountsByOwner RPC method was incorrect, showing only one required parameter when two are actually required. This led to API errors when users omitted the second parameter.

Summary of Changes

• Updated the introduction to clearly state that two parameters are required
• Modified the Parameters section to show two required parameters:
  1. The owner's public key (previously incorrectly labeled as "delegate")
  2. An object specifying either mint or programId (previously marked as optional)
• Added a note emphasizing that the second parameter must include either mint or programId
• Updated the code sample to demonstrate both mint and programId usage

These changes ensure the documentation accurately reflects the API's requirements, preventing confusion and errors for developers using the getTokenAccountsByOwner method.

Fixes #520