feature(go): add support for multiple model versions

[hugoaguirre]

Adding the support for multiple model versions and grouping the versions in the model metadata.

Gemini models being rendered in Dev UI frontpage

Model versions being grouped in the Dev UI

Playing around with gemini-1.5-flash-8b-latest

Checking raw request

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)

[hugoaguirre]

Hi @pavelgj, @apascal07

Let me know your opinion about this approach.
I wanted to keep the model definition as it previously was because I think it was very simple and verbose.

The only changes added were:

• Rewrote how the known models are defined in the plugins (adding a new struct named: ai.ModelDetails that encapsulates the model capabilities and its versions)
• ai.ModelMetadata was updated to add model versions so they can be grouped together

[alonsopec89]

this hardcoded strings of the version management can become a bit complicated to maintain, and since we are using the same ones in googleai and vertexai, I think it would be good to have in some constants file, maybe in the genkit package or another new one, so that it is used here and in vertexai

[hugoaguirre]

Good observation @alonsopec89.

I was looking at how things were implemented in Genkit JS and plugins are in charge of defining the models they use regardless if more plugins are using the same models. e.g. js vertex and js googleai.

About placing these model definitions in genkit package... my understanding is that Genkit should be model-agnostic so I believe that's the reason behind why plugins are defining their models on their packages.