chore(docs): add task delete docs to site content

site/content/docs/commands/task-delete.md

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+# task delete
+```
+$ copilot task delete
+```
+
+## What does it do?
+`copilot task delete` removes the resources created by a one-off task.
+
+Generally, the steps involved in `task delete` are:
+
+1. Stop all running instances of the task.
+2. Empty the ECR repository for the task.
+3. Delete the CloudFormation stack, including the ECR repo, log group, and ECS Task Definition.
+
+!!!info
+    1. Tasks created with versions of Copilot earlier than v1.2.0 cannot be stopped by `copilot task delete`. Customers using tasks launched with earlier versions should manually stop any running tasks via the ECS console after running the command. 
+    2. If you are using the `--default` flag, you cannot also specify the `--app` or `--env` flags. 
+
+## What are the flags?
+```
+  -a, --app string    Name of the application.
+      --default       Optional. Delete a task which was launched in the default cluster and subnets.
+                      Cannot be specified with 'app' or 'env'
+  -e, --env string    Name of the environment.
+  -h, --help          help for delete
+  -n, --name string   Name of the service.
+      --yes           Optional. Skips confirmation prompt.
+```
+## Example
+Delete the "test" task from the default cluster.
+```
+$ copilot task delete --name test --default
+```
+
+Delete the "db-migrate" task from the prod environment.
+```
+$ copilot task delete --name db-migrate --env prod
+```
+
+Delete the "test" task without confirmation prompt.
+```
+$ copilot task delete --name test --yes
+```