feat(core): diesel models and db interface changes for call_back_mapper table

[prasunna09]

Type of Change

• [ ] Bugfix
• [x] New feature
• [ ] Enhancement
• [ ] Refactoring
• [ ] Dependency updates
• [ ] Documentation
• [ ] CI/CD

Description

Created call_back_mapper table and implemented interface for DB operations. this is added for network tokenization webhooks feature. Since this is generic, any kind of data (excluding sensitive info) can be stored.

db changes -

Network tokenization webhook feature use case - no merchant id is passed from token requestor, so network_token_requestor_ref_id is stored in this table along with merchant_id

Additional Changes

• [ ] This PR modifies the API contract
• [ ] This PR modifies the database schema
• [ ] This PR modifies application configuration/environment variables

Motivation and Context

How did you test it?

This PR is only meant for creating new call_back_mapper table and doesn't interfere with any existing flows.

Checklist

• [x] I formatted the code cargo +nightly fmt --all
• [x] I addressed lints thrown by cargo clippy
• [x] I reviewed the submitted code
• [ ] I added unit tests for my changes where possible