[FEATURE] Allow configuring the default Bedrock modelId and region using environment variables

[massi-ang]

Problem Statement

Strands provide a simple and streamlined way to create agents with a single line of code

agent = Agent()

Unfortunately, this only works if the code is run in an environment where the AWS_DEFAULT_REGION is a US region, since the default Bedrock model Id which is used by this code is us.anthropic.claude-sonnet-4-20250514-v1:0

Proposed Solution

Create two environment variables that can be used to override the standard settings:
STRANDS_BEDROCK_MODEL_ID
STRANDS_BEDROCK_REGION

Use Case

Provide a simple way to run all the sample code in regions other than US an possibly with different models without having to modify the code.

Alternatives Solutions

No response

Additional Context

No response

[dbschmigelski]

Hi @massi-ang, this should no longer be an issue with #835. We did not add env var support but the US region bias is now removed.