namespace the env vars

[huntharo]

Currently the env vars used to control the adapter are common names that may overlap with applications.

With the exception of PORT, perhaps the existing names should be deprecated (but still work until 1.0) and new namespaced versions should be introduced, such as LAMBDA_ADAPTER_ASYNC_INIT.

I'm opening this issue because I'm about to submit a PR with COMPRESSION as a config env var and it seems wrong to grab that name, but I also don't want to submit a PR with the only namespaced env var.

[bnusunny]

Thanks! We are thinking about this as well. We plan to namespace the environment variables with AWS_LWA_ and support both formats until v1.0.