[Feature Request]: Ability to add custom Tags at the Environments level

[libert-xyz]

Describe your idea/feature/enhancement

For billing and cost allocation purposes we want to be able to add custom tags in the Environments.

Proposal

Currently the Environments only sets two custom tags

  Key                  Value
  ---                  -----
  copilot-application  my-app
  copilot-environment  staging

We want to be able to add a custom tag in the manifest.yml file

something like

name: staging
type: Environment
http:
  hosted_zone: ZNZO1xxxx
  public:
    certificates:
      - arn:aws:acm:xxxx
network:
  vpc:
    id: vpc-xxxx
    subnets:
      public:
        - id: subnet-xxxx
        - id: subnet-xxxx
      private:
        - id: subnet-xxxx
        - id: subnet-xxxx
## Custom tags
tags:
  Company: ACME