support custom profile

[softprops]

What did you implement:

This allows you override the default behavior of building a release profile and allows you to set a named profile. Atm the only useful one one cargo supports is "dev"

custom:
   rust:
     profile: dev

# or
functions:
  test:
    rust:
       profile: dev
    handler: your-cargo-package-name
    events:
      - http:
          path: /test
          method: GET

Closes: #xxx

How did you verify your change:

tbd

What (if anything) would need to be called out in the CHANGELOG for the next release:

ability to build rust lambda with dev profiles

[softprops]

@maxcountryman nice catch. You are totally right. I should be able to get back to this pull this weekend

[softprops]

I'll try to make that part of an integration test