Better error experience when configuration file created with type="unknown"

[sagerb]

The interface allows the file picker within new deployment flow to select files for which our inspection cannot determine the content-type value (so it sets it to an invalid (according to the schema) "unknown" value).

This is a screenshot of what the user is presented with:

Some additional details:

• GET configuration does return some info within the configurationError that we process within the UX:

  {
    "configurationName": "multi-type-RKIG",
    "configurationPath": "/Users/billsager/dev/publishing-client-alt/test/sample-content/multi-type/.posit/publish/multi-type-RKIG.toml",
    "configurationRelPath": ".posit/publish/multi-type-RKIG.toml",
    "projectDir": "test/sample-content/multi-type",
    "error": {
      "code": "tomlValidationError",
      "msg": "type: value must be one of \"html\", \"jupyter-notebook\", \"jupyter-voila\", \"python-bokeh\", \"python-dash\", \"python-fastapi\", \"python-flask\", \"python-shiny\", \"python-streamlit\", \"quarto-shiny\", \"quarto\", \"r-plumber\", \"r-shiny\", \"rmd-shiny\", \"rmd\"",
      "operation": "",
      "data": {}
    }
  },

It is thought that we could handle this error much more specifically and improve the user experience.