[Feature Request] Chalice Workspaces for consistent environment across functions

Idea Reference : [Cargo Workspaces](https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html)

When working with multiple chalice-managed lambdas, it would be helpful to have a consistent environment so that it there are no unexpected inconsistent behaviours.

One way to do that would be to have a common lambda layer that handles all the dependencies across multiple functions. This will allow developers to update and manage functions both as individual elements or as a batched atomic transaction from within the same venv.

The issue names no source files, tests, or entry points. Begin by reviewing how Chalice currently manages dependencies across multiple functions, then examine the Cargo Workspaces reference and Lambda layers; done means consistent environments with both per-function updates and atomic multi-function updates.

Written by the indexing model from the issue text.