feat: add additional 6 document API methods and update README with examples

[Siddhantsingh1230]

Summary

This PR adds six new API methods to the frappe-js-sdk for interacting with Frappe documents. Additionally, the README has been updated to include usage examples for these methods.

Changes Introduced

• Added the following API methods:

  1. getValue - Fetch single or multiple field values from a document based on filters.
  2. setValue - Set single or multiple field values in a document.
  3. renameDoc - Rename an existing document.
  4. getSingleValue - Retrieve a field value from a Single Doctype.
  5. submit - Submit a document.
  6. cancel - Cancel a document.

• Updated db/types

  • Add FieldName type to support new API methods.

• Updated the README with:

  • Code examples for the newly added methods.
  • Parameter descriptions and expected outputs.

How to Test

• Call each method with appropriate parameters and ensure they return expected results.
• Verify that the README examples execute correctly without errors.

Notes

• These changes enhance the SDK’s usability by providing essential document operations.
• Ensure that backend permissions allow necessary CRUD operations for testing.

@nikkothari22