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