GET /kapacitor/v1/tasks does not return task template-id

[sranka]

Actual behavior:

GET /kapacitor/v1/tasks does not return template-id in the returned task list, it is not a supported field per https://github.com/influxdata/kapacitor/blob/v1.6.1/services/task_store/service.go#L487 . template-id is however properly returned when getting a particular task (https://github.com/influxdata/kapacitor/blob/v1.6.1/services/task_store/service.go#L1134).

Expected behavior:

• template-id is OOTB returned in GET /kapacitor/v1/tasks
• the kapactior swagger file adds (a read-only) template-id to the Task object, it should be already there since the get task operation returns it.

Rationale:
Tasks that were created from a template must be read-only in chronograf so that the users are not confused with something that cannot be effectively edited (in chronograf), this is already fixed in influxdata/chronograf#5805 . Additionally, templated tasks cannot be ever chronograf rules (their TICKScripts were not created by chronograf). This is already taken into account in the chronograf code, but it does not work prefectly because of the missing template-id in the task list. Chronograf now has to spend useless time with parsing and processing such templated tasks. If the task TICKScript can be parsed as a chronograf rule, the task then appears in the list of chronograf rules and can be clicked as a rule. The user is then however informed that it is not a chronograf rule that could be possibly managed. Fixing this issue would also fix such a weird user experience on the chronograf side.