feat: add tag resource

[someone-stole-my-name]

Add test cases

Description

Allows managing compute tag resources.

Motivation and Context

We need tags to manage vulnerabilities.

How Has This Been Tested?

On our own tenant with TF_ACC=1 go test -v ./internal/provider/... -run TestAccTagConfig and TF:

resource "prismacloudcompute_tag" "test" {
  name        = "test"
  assignment {
    id            = "CVE-2021-29923"
    resource_type = "image"
  }
}

Terraform will perform the following actions:

  # prismacloudcompute_tag.test will be created
  + resource "prismacloudcompute_tag" "test" {
      + color = "#A020F0"
      + id    = (known after apply)
      + name  = "test"

      + assignment {
          + id            = "CVE-2021-29923"
          + package_name  = "*"
          + resource_type = "image"
        }
    }

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes if appropriate.
• [x] All new and existing tests passed. New tests pass, existing ones are broken 😢

[welcome-to-palo-alto-networks[bot]]

:tada: Thanks for opening this pull request! We really appreciate contributors like you! :raised_hands: