Added layer option for deploy function update-config

[Kivol]

What did you implement:

Closes #5786

How did you implement it:

Added the processing code for layer option, and the corresponding test and validations

How can we verify it:

I've verified myself that this layer update config works fine.

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[pmuens]

Great! Thanks for working on this @Kivol 👍

Just tested it today and it works as expected. LGTM

Here's the config I used to test it:

service: test

provider:
  name: aws
  runtime: provided

functions:
  hello:
    handler: handler.hello
    layers:
      - arn:aws:lambda:us-east-1:553035198032:layer:nodejs11:8
      # - arn:aws:lambda:us-east-1:553035198032:layer:nodejs10:3

[vaibhav3patil]

Can we adding the functionality that could point to the latest layer by default ?
giving version number in ARN can be some manual work if deploy a new version of lambda layer, or how I can refer the latest version fo lambda layer in serverless even if creating new version I do not want to change in my serverless.yml ?