add optional id to plugins

[srivastava-diya]

Description

This PR makes EvaluationPlugin instances JSON-serializable by introducing an optional id identifier.

Solves : #110

Changes Made

1. Types & Base Plugins:
   • Updated the EvaluationPlugin interface in lib/experimental.d.ts to include an optional id?: string property.
   • Added id properties to the BasicOutputPlugin, DetailedOutputPlugin, and AnnotationsPlugin class declarations.
   • Updated README.md to reflect the new id field in the EvaluationPlugin documentation.
2. Keyword-Specific Plugins:
   • Added an id property to the plugins defined in the dynamicRef, unevaluatedProperties, and unevaluatedItems keyword handlers.
   • Added an id property to the draft-2020-12/dynamicRef keyword handler.