Expose Template Task association via the API and CLI

Kapacitor needs to make getting the list of tasks for a template and the template for a list of tasks easy.

Currently the template information is exposed only through a GET request on the task resource.

I propose we make a few changes:

1. Add the `template` field to the `/tasks?` endpoint, (this is really a bug and needs to be fixed anyway)
2. Add a `/templates/tempalte_id/tasks` endpoint which lists the tasks associated with the template.
3. Expose both of these through the CLI.

Start by tracing the existing GET task resource and the `/tasks?` and `/templates/:template_id/tasks` API entry points, then find the corresponding CLI commands. Confirm how task-template associations are currently represented. Done means the task listing includes template information, templates can list associated tasks, and both behaviors are available through the CLI.

Written by the indexing model from the issue text.