Add a config property descriptor along with a custom resolver and validators

[ubaskota]

Issue #, if available:

This PR adds a ConfigProperty descriptor that serves as the central instrument for configuration resolution. The descriptor is responsible for resolving config values from sources, applying custom resolvers for complex resolutions, validating values, caching them, and facilitating value updates.

The ConfigProperty descriptor implements the Python descriptor protocol to provide:

• Lazy resolution
• Validation
• Caching
• Custom resolver
• Source tracking

Initial config variables:

• region - demonstrates simple resolution
• retry_strategy - demonstrates complex resolution (aggregates retry_mode and max_attempts)

These two variables ensure that the design handles both simple and complex resolution.

Tests

• Verified that the unit tests for config property, validators and custom revolvers pass successfully.

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