[Feature]: Document bedrock new flags

[AlexsJones]

Checklist

• I've searched for similar issues and couldn't find anything matching
• I've discussed this feature request in the K8sGPT Slack and got positive feedback

Is this feature request related to a problem?

Yes

Problem Description

Bedrock now requires --providerRegion set on auth add command
It can be overridden dynamically with AWS_DEFAULT_REGION env, this needs documenting.

THESE MUST BE REGIONS BEDROCK IS ENABLED IN

Solution Description

example

k8sgpt auth add -b amazonbedrock -m anthropic.claude-instant-v1 --providerRegion eu-central-1

``

### Benefits

Clearer docs for amazon bedrock etc etc

### Potential Drawbacks

_No response_

### Additional Information

_No response_