fix: defer keyword in json schema

[calvinmclean]

This fixes a few issues with JSON schema validation when using the defer keyword.
It adds a defer_call object that is used alongside cmd_call and for_call. Then, defer is removed from the cmd_call.

Example Taskfile:

version: "3"

tasks:
  integration-test:
    desc: Startup docker resources and run integration tests. Cleanup when done.
    dir: ./garden-app
    cmds:
      - docker compose -f ../deploy/docker-compose.yml --profile test up -d
      - defer: docker volume rm deploy_influxdb
      - defer: docker compose -f ../deploy/docker-compose.yml --profile test down
      - sleep 15
      - go test -race -covermode=atomic -coverprofile=integration_coverage.out -coverpkg=./... ./integration_tests

Errors:

Incorrect type. Expected "boolean".
Missing property "cmd".

[ydarma]

Actually the correct type seems to be "#/definitions/3/cmd"

[andreynering]

Merged with adjustments at c42bc69. Thank you both!

We should not use #/definitions/3/cmd here because defer is only a subset of that. I needed to add support for defer: { task: foobar }, though.