pkg/handlers: implement client side timeouts for running tasks

[aleh-null]

Handles client side timeouts set in the request headers hide-org/hide-sdk#26
Issue #150

curl --request POST \
  --url http://localhost:8080/projects/69qtxbYaQ5/tasks \
  --header 'X-Timeout-Seconds: 10' \
  --header 'content-type: application/json' \
  --data '  {
      "command": "sleep 50"
  }'

returns request timed out