[FR] Add support for checking/validating provided config file

[rustycl0ck]

Instead of detecting errors in parsing jsonpath or in extracting values at runtime, there should be an option to 1) run config file syntax check separately without running the exporter server 2) check config file syntax at startup and exit if validation fails

These checks/validation can include things:

• confirm that all the jsonpath syntax fields are valid expressions
• if a sample data json file is available, check the config file parsing against the data file independently (this will allow users to fix their config files faster and also will help them in figuring out alternate approaches to achieve their metric parsing)
• confirm that module.valid_status_codes has valid HTTP status codes
• confirm that module.http_client_config has valid values
• confirm that provided metric types and value types are valid enum strings
• if/when available, regex expressions are valid (based on feat: filter metric value using regex #240)