expose the listModels call

[devoncarew]

• expose the listModels call
• fix consider exposing the ListModels API call #93
• rev to a new major version as this is an api addition

This exposes model.listModels as a static method on GenerativeModel. The user needs to explicitly pass the api Key to this static method (instead of passing it into the GenerativeModel ctor as for the other calls).

I expose ApiClient? apiClient as a param as well for testability; this does make for a kludgy method sig (w/ params String apiKey, int? pageSize, String? pageToken, http.Client? httpClient, and ApiClient? apiClient).

[natebosch]

I'll start a discussion thread about this - it's not present in the other SDKs I checked and I'm not sure if this is a discrepancy we'd be worried about.

[devoncarew]

I'll start a discussion thread about this - it's not present in the other SDKs I checked and I'm not sure if this is a discrepancy we'd be worried about.

sgtm; note that this is documented in the REST protocol. And the motivating real for this use case is that multiple times I've gotten error messages back from the server - 'models/xxx is not found for API version v1, or is not supported for GenerateContent. Call ListModels to see the list of available models and their supported methods'; its definitely a bit of a semantic mis-match to give that error to the user but to provide no way for them to list the models / call the indicated method.

[devoncarew]

It looks like it's exposed by the python SDK:

https://ai.google.dev/api/python/google/generativeai/list_models

[devoncarew]

Dropping this PR as I believe the python (and REST) SDKs are intended to fully expose the APIs - including for admin functions - and the other language SDKs are intended to be more client SDKs. Happy to re-open if we think this is worth exposing.