fix(go/plugins/googlegenai): Update gemini models

[edwrdc]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[edwrdc]

@hugoaguirre Hi, can you take a look at this. Thanks.

[hugoaguirre]

Hi @edwrdc, thanks for the contribution. Actually, there's no longer need of doing this for recent models.

You can type the name of the model you want to use and it should be available for use.

Either you set it using WithDefaultModel during Genkit init or using .WithModelName() helper function in the Generate() call.

[edwrdc]

Ah, cool. Thanks for the heads up! I'll go ahead and close the PR then.