chore(auth): use FastAPI's HTTPBearer for JWT token extraction

[Roman505050]

Applicable issues

• fixes jwt field of the request doesn't contain JWT, but Bearer: JWT #196

Description of changes

This pull request improves authentication handling in the FromRequestDeploymentMixin class by integrating FastAPI's HTTPBearer authentication scheme. Key updates include:

• aidial_sdk/deployment/from_request_mixin.py: Imported HTTPBearer from FastAPI to support bearer token authentication.
• aidial_sdk/deployment/from_request_mixin.py: Introduced a _bearer class attribute initialized with HTTPBearer(auto_error=False) to enable optional error raising on missing/invalid tokens.
• aidial_sdk/deployment/from_request_mixin.py: Refactored the from_request method to use _bearer for token extraction. The method now processes the Authorization header using _bearer and extracts the token from the resulting credentials.

These changes address an issue where the JWT token was not correctly retrieved from the Authorization: Bearer header.

Checklist

• Title of the pull request follows Conventional Commits specification

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