[Feature] support HEAD method for endpoints that already support GET method

For checking access to endpoints f.ex it would be great if the kapacitor endpoints that support the GET method, also supported the HEAD verb. At least for the kapacitor/v1/tasks, it returns 404 when I query it using the HEAD verb, but returns all tasks if I do a GET call.

Use the GET handling for kapacitor/v1/tasks as the reference and trace how HTTP methods are routed for endpoints that support GET. Verify that HEAD requests succeed without returning a response body while existing GET behavior remains unchanged, including the reported tasks endpoint. Add or run the relevant endpoint tests if they are present.

Written by the indexing model from the issue text.