Changes to Start a grok computer use task

added subschema #4 to the sessionOptions/credentials/items request property oneOf list

added the new optional request property sessionOptions/credentials

added the new optional request property sessionOptions/proxyRoutes

added the new optional request property sessionOptions/webBotAuth

added the new optional request property sessionOptions/enableWebMcp

the llm request property default value changed from grok-4.5 to grok-4.7

added the new grok-4.6 enum value to the request property llm

added the new grok-4.7 enum value to the request property llm

added the new us enum value to the request property sessionOptions/region

endpoint added