Update Inference specification for Hugging Face's completion and chat completion tasks

[Jan-Kazlouski-elastic]

This PR is for changes to specification caused by elastic/elasticsearch#127254:

Extended Task Support:

• Added completion and chat_completion tasks to the list of supported Hugging Face tasks.

Model Requirements for Chat Tasks:

• Updated documentation to describe specific requirements for using chat_completion and completion tasks, including model compatibility with the OpenAI API format and usage guidelines for serverless vs. dedicated endpoints.

New Configuration Parameters:

• Introduced optional model_id field in Hugging Face service settings, applicable to completion and chat_completion tasks.

Rate Limit Clarifications:

• Updated rate_limit documentation to clarify default behavior and guidance for tuning based on deployment specifics.

Documentation Fixes:

• Corrected typos in existing text_embedding request examples.

Additional actions

• Signed the CLA

• Executed make contrib

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
inference.chat_completion_unified	⚪	Missing test	Missing test
inference.completion	⚪	Missing test	Missing test
inference.delete	⚪	Missing test	Missing test
inference.get	🟢	1/1	1/1
inference.inference	⚪	Missing test	Missing test
inference.put_alibabacloud	⚪	Missing test	Missing test
inference.put_amazonbedrock	⚪	Missing test	Missing test
inference.put_anthropic	⚪	Missing test	Missing test
inference.put_azureaistudio	⚪	Missing test	Missing test
inference.put_azureopenai	⚪	Missing test	Missing test
inference.put_cohere	⚪	Missing test	Missing test
inference.put_elasticsearch	⚪	Missing test	Missing test
inference.put_elser	⚪	Missing test	Missing test
inference.put_googleaistudio	⚪	Missing test	Missing test
inference.put_googlevertexai	⚪	Missing test	Missing test
inference.put_hugging_face	⚪	Missing test	Missing test
inference.put_jinaai	⚪	Missing test	Missing test
inference.put_mistral	⚪	Missing test	Missing test
inference.put_openai	⚪	Missing test	Missing test
inference.put_voyageai	⚪	Missing test	Missing test
inference.put_watsonx	⚪	Missing test	Missing test
inference.put	⚪	Missing test	Missing test
inference.rerank	⚪	Missing test	Missing test
inference.sparse_embedding	⚪	Missing test	Missing test
inference.stream_completion	⚪	Missing test	Missing test
inference.text_embedding	⚪	Missing test	Missing test
inference.update	⚪	Missing test	Missing test

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