feat: Support AWS_BEARER_TOKEN_BEDROCK

• I have looked for existing issues (including closed) about this

Feature Request

Support AWS_BEARER_TOKEN_BEDROCK for Bedrock inference calls.

Motivation

Bearer tokens make prototype iteration slightly easier when working with Bedrock.

Proposal

Haven't looked deeply; this might "just work" if this crate uses the aws-sdk-bedrock crate.

Alternatives

The standard AWS_SECRET_ACCESS_KEY works for production workloads.