Add support for environment token provider for services whose SigV4 signing names are bedrock

[ysaito1001]

Motivation and Context

Adds support for environment token provider for AWS services whose SigV4 service signing name matches bedrock. Setting this environment variable, AWS_BEARER_TOKEN_BEDROCK, allows SDKs to prefer the httpBearerAuth auth scheme and to retrieve a Token value from the said environment.

Description

Customers would use the environment variable in question like so:

    // export AWS_BEARER_TOKEN_BEDROCK=my-token

    let sdk_config = aws_config::defaults(BehaviorVersion::latest()).load().await;

    let bedrock_client = aws_sdk_bedrock::Client::new(&sdk_config);
    // call an operation on `bedrock_client`...

Under the hood, this is equivalent roughly to

    let sdk_config = aws_config::defaults(BehaviorVersion::latest()).load().await;
    let bedrock_config = aws_sdk_bedrock::config::Builder::from(sdk_config)
        .auth_scheme_preference([HTTP_BEARER_AUTH_SCHEME_ID])
        .token_provider(Token::new("my-token", None))
        .build();

    let bedrock_client = aws_sdk_bedrock::Client::from_conf(bedrock_config);
    // call an operation on `bedrock_client`...

This behind-the-scenes convenience is implemented in impl From<&SdkConfig> for Builder, similar to how a service-specific environment is implemented for the endpoint URL.

However, impl From<&SdkConfig> for Builder implies that customers need to create a service client from SdkConfig (typically through ConfigLoader::load) in order to take advantage of the environment variable. If customers create the service client directly from the service config builder, the environment variable will not be applied, i.e.

    // export AWS_BEARER_TOKEN_BEDROCK=my-token

    let bedrock_config = aws_sdk_bedrock::Config::builder()
        // other configurations
        .build();

    let bedrock_client = aws_sdk_bedrock::Client::from_conf(bedrock_config);
    // `bedrock_client` neither prefers HTTP_BEARER_AUTH_SCHEME_ID nor sets a Token with my-token.

Testing

• Added integration tests for bedrockruntime (whose model is already checked in to aws/sdk/aws-models)

Checklist

• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[landonxjames]

Nice, didn't know this was possible!

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Client Test (ignoring whitespace)
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.