Update docs for UBB

[ntrogh]

This pull request updates the Copilot documentation and related configuration to reflect the transition from "premium requests" to "AI credits" for usage-based billing and model consumption.

The changes clarify how AI credits are consumed, provide practical tips for optimizing credit usage, and update references and terminology throughout the docs.

Additionally, new guidance and links are added to help users manage and reduce AI credit consumption.

Key changes include:

Documentation terminology and billing updates:

• Replaced references to "premium requests" with "AI credits" across multiple documentation files, including details on how credits are consumed, how different models and features affect credit usage, and links to usage-based billing documentation.

Guidance on optimizing AI credit usage:

• Added new documentation links and tips throughout the docs to help users optimize and manage AI credit consumption, including context compaction, tool selection, and session management strategies.

Other documentation improvements:

• Clarified language and updated examples in best practices and feature guides, including the impact of context management and tool usage on credit consumption.

Implements #9774, #9775

[ntrogh]

@cwebster-99 Did you mean to say "cost more per tokens"? Sounds weird.