feat: Implement tag triggers for docker_tag resource (#702)

docs/resources/tag.md

@@ -20,6 +20,10 @@ Creates a docker tag. It has the exact same functionality as the `docker tag` co
 - `source_image` (String) Name of the source image.
 - `target_image` (String) Name of the target image.
 
+### Optional
+
+- `tag_triggers` (Set of String) List of values which cause the tag to be (re)created. This is useful for triggering a new tag when the source image changes.
+
 ### Read-Only
 
 - `id` (String) The ID of this resource.

internal/provider/resource_docker_tag.go

@@ -27,6 +27,14 @@ func resourceDockerTag() *schema.Resource {
 				Required:    true,
 				ForceNew:    true,
 			},
+			"tag_triggers": {
+				Type:        schema.TypeSet,
+				Description: "List of values which cause the tag to be (re)created. This is useful for triggering a new tag when the source image changes.",
+				Optional:    true,
+				ForceNew:    true,
+				Elem:        &schema.Schema{Type: schema.TypeString},
+				Set:         schema.HashString,
+			},
 		},
 	}
 }