Add parameter validation to RapidApi class constructor

This issue tracks the enhancement to add parameter validation for , , and in the class constructor, as discussed in PR https://github.com/angelxmoreno/rapidapi-node-sdk/pull/3 and specifically in this comment: https://github.com/angelxmoreno/rapidapi-node-sdk/pull/3#discussion_r1477126073

Adding these validations will ensure that the class is instantiated with all necessary configuration parameters, preventing runtime errors related to missing configurations.

Start with the RapidApi class constructor and review PR #3, especially comment discussion_r1477126073, to identify the three configuration parameters requiring validation. Done means the constructor rejects missing required configuration and prevents the described runtime errors; the issue does not name a test or source file to run.

Written by the indexing model from the issue text.