tools/unitctl: implement application subcommand

[avahahn]

This MR addresses #1280 and #1279 by providing a subcommand unitctl app that provides two options:

• unitctl app list: returns a list of running applications

  $ unitctl app list -t json-pretty
  {
  "wasm": {
  "type": "wasm-wasi-component",
  "component": "/www/wasmapp-proxy-component.wasm"
  }
  }

• unitctl app <NAME> reload: reloads an application by name

  $ unitctl app reload wasm -t json-pretty
  {
  "success": "Ok"
  }

This MR also adds missing wasm and wasi application schemas to the OpenAPI spec.