[Feat]: add AWS STS assume-role and SigV4 signing for Bedrock

[samadpls]

Fixes #690

• Added support for AWS credentials configuration in the schema and configuration files.
• Introduced functions to retrieve AWS credentials from the environment and sign requests using AWS Signature Version 4.
• Updated the StreamContext and FilterContext to handle AWS credentials and integrate with Bedrock services.
• Added new error handling for AWS-related operations.
• Updated Cargo.toml files to include necessary AWS dependencies and features.

[san81]

Making use of official AWS Rust crates that handle SigV4 signing will be a better option here. Like

Cargo dependencies (crates/common/Cargo.toml)

[dependencies]
aws-sigv4 = "1"
aws-credential-types = "1"
aws-types = "1"
http = "1"
bytes = "1"

and for STS and caching

aws-sdk-sts = "1"
aws-config = "1"

We can replace the custom signer added in this PR with a simple thin wrapper based on this official aws crate.

[samadpls]

Thanks for the feedback @san81. I am working on the updates now and will address the points you raised.