Version 1.2.1 features and fixes

[tmcgilchrist]

• Bump lower bound to 4.08 to include Uri 4.1 fixes for escaping Add basic github-action. #104
• Generate AWS Lambda AWS lambda #108
• Migrate CI to github actions Add basic github-action. #104
• Need AWS Lambda tests and example usage
• Align ENV variable usage with official AWS client usage Rename the Unix Env variables expected in tests. #111
• Include AWS documentation for services in generated code
• Bump ppx_tools_versioned lower bound to 4.08, Better option to remove the dependency Stop to migrate and omit < 4.08 support #126
• Support for signing requests with assume_role tokens STS: add support for signing requests with assume_role tokens #117
• Add KMS support KMS: add KMS support #118

In the interests of visibility these are the pieces I'm working on for the next minor release of ocaml-aws.

EDIT
Removing the aws-lambda support from this release, it requires a larger re-write than I expected.