feat: Implementation of Exchange updater console app

[AjayP123]

Changes Included the below components and Unit test cases

• ExchangeRateService

  • Orchestrates fetching exchange rates for requested currencies.
  • Checks daily rates cache first; if some currencies are missing, checks monthly rates cache.
  • Only calls the monthly API if needed, minimizing unnecessary API calls.
  • Logs warnings for currencies not found in either source.

• CnbRatesCache

  • Wraps IMemoryCache for caching daily and monthly rates.
  • Uses a unique cache key and an expiration factory for each cache instance.
  • Handles cache hits, misses, and logging.
  • Fetches and caches data using a provided factory function.

• CzechApiClient

  • Handles HTTP GET requests to the Czech National Bank API.
  • Logs requests and responses, and handles errors gracefully