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