Please explain the motivation behind the feature request.
While registering a custom provider (to my local ramalama server), I noticed that it is required to add an API Key to the custom provider, whoever, in ramalama (at least), the usage of API Key is optional. I think that goose should allow for empty API Key in case the custom provider does not need/accept it.

Describe the solution you'd like
Make the API Key field during the custom provider registration optional

Describe alternatives you've considered
An alternative was putting an random string while registering & using the custom provider.

Additional context
None.

• I have verified this does not duplicate an existing feature request