feat(signature-v4a): create SignatureV4a JavaScript implementation

[kuhe]

moved from #1250 so I have write access.

The goal of the original PR is to have a sigv4a implementation without the CRT, so it can be used in browsers.

[kuhe]

• tag https://github.com/bmaggia as author in the squash commit before merging

[zeyad001]

Looking forward to this functionality

[justin-masse]

Any movement on this @kuhe? We cannot use the current sigv4a signing with the aws-crt dependency due to incompatibility with js build tools.

[kuhe]

Unfortunately, I do not have an estimate as to when this will be available.

It is in a state of awaiting an internal review, due to its relation to a security feature.

[justin-masse]

Unfortunately, I do not have an estimate as to when this will be available.

It is in a state of awaiting an internal review, due to its relation to a security feature.

Darn, this is definitely something we're waiting for so we can use this in lambda with JS build tools since the aws-crt package has relative pathing to binaries.