Allow to select alias for Provisioned Concurrency

Feature Proposal

Allow selecting Provisioned Concurrency Alias

Description

I have been trying to setup provisioned concurrency using the Canary Deployment plugin, but both of them require the use of alias and do not allow for overlaps. Being able to select the alias for provisioned concurrency will allow for reusing the same alias used for the canary deployment.

As of right now when setting the canary plugin deployment alias to provisioned just makes provisioned concurrency not able to function because it will say the alias already exists.

I am not honest if it would be best to fix the current paradigm inside here or in the canary plugin: https://github.com/davidgf/serverless-plugin-canary-deployments

1. What is the use case that should be solved. The more detail you describe this in the easier it is to understand for us.
   The use case is being able to set the alias of the provisioned concurrency or allow reusing an existing alias that is in use. Example above explains.

2. Optional: If there is additional config how would it look

functions:
  main: # The name of the lambda function
    name: my-func
    provisionedConcurrency: 3
    provisionedAlias: "Active"

No file or test is named. Start by locating the handling for the provisionedConcurrency function setting, then review the linked Canary Deployment plugin's alias behavior. Done means the configuration can select or safely reuse the requested alias without the existing-alias conflict in the described deployment scenario.