feat(aws): add AWS Lambda function

[mogery]

Summary:
This PR adds the ability to run tailcall on AWS Lambda.

Issue Reference(s):
Fixes #874
/claim #874

To-do:

• Implement configuration

Build & Testing:

• I ran cargo test successfully.
• I have run ./lint.sh --mode=fix to fix all linting issues raised by ./lint.sh --mode=check.

Checklist:

• I have added relevant unit & integration tests.
• I have updated the documentation accordingly.
• I have performed a self-review of my code.
• PR follows the naming convention of <type>(<optional scope>): <title>

[mogery]

Implementation details:

• Deployment to Lambda is done via Terraform.
  • The GraphQL definition is bundled with the image at deploy-time.
• There's no built-in KV store for AWS like there is in Cloudflare, so I built a simple Cache provider based on HashMap.
• The current implementation of LambdaFileIO reads from the filesystem, instead of, say, an S3 bucket, since it's needed to retrieve the GraphQL definition from the image bundle.

Questions:

Should the Terraform deployment code live in this repo?

The DX of a Lambda deployment is pretty bad right now. A dev has to:

1. Install Rust, Terraform, Python and cargo-lambda
2. Add AWS credentials to environment variables
3. Clone this repo
4. Build the lambda crate with cargo-lambda
5. Write a GraphQL definition into lambda/deploy/config.graphql
6. Run terraform init && terraform apply

We could move this to an external repo, and I can make the CI build Lambda images and put it in Releases, and the Terraform config can be adapted to download it. With that, the DX would be the following:

1. Install Terraform
2. Add AWS credentials to environment variables
3. Clone that repo
4. Write a GraphQL definition into lambda/deploy/config.graphql
5. Run terraform init && terraform apply

This is, in my opinion, much better. It also lets devs fork the repo and manage their own deployment schema on GitHub.

[mogery]

Adapted to the new TargetRuntime.

[mogery]

...wtf are these codecov errors

[meskill]

...wtf are these codecov errors

yeah, strange, but don't bother about it, it won't affect pr merge