[CI-2304] Spinner output configuration

[tothszabi]

The self hosted agent setup uncovered a path in the CLI where it was not using structured logging but instead was writing directly to the stdout. The build log grouping service was receiving such content:

[
   ...
   {
      "timestamp":"2023-12-04T16:15:17.7254-06:00",
      "type":"log",
      "producer":"bitrise_cli",
      "level":"normal",
      "message":"You can find more information about stepman on its official GitHub page: https://github.com/bitrise-io/stepman\n"
   },
   "Installing...",
   {
      "timestamp":"2023-12-04T16:15:18.233691-06:00",
      "type":"log",
      "producer":"bitrise_cli",
      "level":"normal",
      "message":"\u001b[32;1m[OK]\u001b[0m stepman (0.16.1): /Users/foreflight/.bitrise/tools/stepman\n"
   },
   ...
]

where the Installing... message is not wrapped into a json object. The root cause of it was the spinner component which was writing directly to the stdout.

After these changes the component generates correct json output:

{"timestamp":"2023-12-05T15:21:52.645225Z","type":"log","producer":"bitrise_cli","level":"normal","message":"Installing...\n"}

I have created a new initialiser which accepts an io.Writer which will be used as the destination.