Selectively build with container for certain resources

### Describe your idea/feature/enhancement

The SAM CLI `build` command lets you pass `--use-container` to build resources inside the corresponding container.

Building in a container usually takes longer, but provides the same platform/native environment for the build process.

I would like to selectively choose which `AWS::Serverless::Function`s (or `Resource`s) to be built inside a container.

### Proposal

Add a `BuildContainer` under `Properties` for `AWS::Serverless::Function`.

Things to consider:
[ ] The [SAM documentation](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification.html) will need to be updated