[Feature] Allow to configure configure tags per backend and or per configuration

[peterschmidt85]

Similar to Terraform's tags, it should be possible to configure tags per backend and or per configuration. These tags should be assigned to any corresponding cloud resources (where it's supported).

Examples:

projects:
  - name: main
    backends:
      - type: was
        creds:
          type: default
        tags:
          my_app_name: dstack
          my_department: 12345
          my_environment: production
          owner: andrey@dstack.ai
          my_project: "${{ project_name }}"
          my_user: "${{ user_name }}"