Move EvCharging schemas to DEG repo

[ameetdesh]

Summary

• Migrates all EV Charging domain schemas from protocol-specifications-new to the DEG specification/schema/ directory
• Updates schema @context URL references across all EV Charging examples and documentation

Changes

New schema directories added:

• specification/schema/EvChargingOffer/v1/ - Charging offer attributes
• specification/schema/EvChargingSession/v1/ - Session state tracking
• specification/schema/EvChargingService/v1/ - Service/item definitions with examples
• specification/schema/EvChargingPointOperator/v1/ - CPO provider attributes

Adds renderer.json for EvChargingService.

Updated references (20+ files):

• All examples/ev-charging/v2/*.json files now point to DEG schema URLs
• docs/implementation-guides/v2/EV_Charging/EV_Charging.md - updated schema links
• scripts/validate_schema.py - updated base URL
• Postman collections regenerated with new URLs

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Closes #180