Add support for multiple Google Model Garden providers for completion and chat_completion tasks

[Jan-Kazlouski-elastic]

This PR adds changes to specification caused by elastic/elasticsearch#135701

Additional actions

• - Signed the CLA
• - Executed make contrib

[github-actions]

Following you can find the validation changes against the target branch for the APIs.

API	Status	Request	Response
bulk	🟢	548/548 → 558/558	566/566 → 576/576
indices.create_data_stream	🟢	121/121 → 131/131	121/121 → 131/131
indices.delete_data_stream	🟢	96/96 → 98/98	96/96 → 98/98
indices.get_sample	🔴	13/13 → 24/24	9/13 → 16/24
indices.get_sample_stats	🔴	14/14 → 26/26	13/14 → 24/26
indices.put_index_template	🔴	130/154 → 140/164	154/154 → 164/164
indices.rollover	🔴	59/59 → 69/69	2/59 → 2/69
search	🔴	2594/2615 → 2593/2612	2615/2615 → 2612/2612

You can validate these APIs yourself by using the make validate target.

[jonathan-buttner]

Could you add examples of the other providers?

That way it'll be more clear when a user needs to include url vs url and streaming_url.

[Jan-Kazlouski-elastic]

Added examples for the rest of the providers.

[jonathan-buttner]

Could you also add in the url and streaming_url field comments which providers require which ones? (basically the same thing we did in the comment in the Java code).

[Jan-Kazlouski-elastic]

Added.

[Jan-Kazlouski-elastic]

@jonathan-buttner your comments are addressed. Could you please take another look at this PR?

[jonathan-buttner]

Thanks for adding these examples. Is there anymore information we can give the user to help aid them in finding these URLs? Is there a general place where they can find them (like after creating the model garden endpoint, go to this tab to find the base url and you'll need to add :streamRawPredict to the end etc).

I'm not sure if the best place for that is here in the examples though.

[Jan-Kazlouski-elastic]

I’ve updated the documentation with the following changes:

• Added more examples covering each provider’s serverless, dedicated, and shared endpoints.
• Included specific URL patterns in the url and streaming_url fields for each example.
• Added details on where to find the variables used to construct these URLs in each example.
• Updated the descriptions of the url and streaming_url fields with general guidance on where to find URL construction information (in the Google Model Garden documentation for the model, or on the endpoint’s Sample request page).