llms/databricks: Add Databricks LLMs service endpoints support

[t0mpl]

Databricks hosts some LLMs and expose API for them.

NB: with the multiplication of model providers, maybe the langchaingo structs formatter should be separate from the client. We will duplicate some code otherwise.

PR Checklist

• [ ] Read the Contributing documentation.
• [ ] Read the Code of conduct documentation.
• [ ] Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
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• [ ] Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. Fixes #123).
• [ ] Describes the source of new concepts.
• [ ] References existing implementations as appropriate.
• [ ] Contains test coverage for new functions.
• [ ] Passes all golangci-lint checks.

[t0mpl]

Hey FluffyKebab, thanks for the review, made the changes you've asked