Feature: Added "enabled" as a feature to FastAPILimiter

[trevorWieland]

enabled: Default value is True which changes no features, but can be set to False. When False, no limiting checks will be done.

Use Cases: For debugging other features of API, excluding the Rate Limiter For enabling/disabling Rate Limiter using an environment variable, for deployment purposes

[trevorWieland]

I tested the results on my local machine, and added some test cases to ensure all '200' results when running the same original tests, but with enabled set to False.

Sorry in advance for any mistakes, this is my first time submitting a pull request in a public repository

[koleror]

Hey there! I would love to see this merged. Any reason it's not?

[long2ice]

Thanks! Please resolve conflicts.