Install-ChocolateyInstallPackage docs/function mismatch

### What You Are Seeing?
Calling Install-ChocolateyInstallPackage for a local .msi without specifying the `-filetype` parameter causes a `ERROR: Exception calling "Start" with "0" argument(s): "The specified executable is not a valid application for this OS platform."`

### What is Expected?
FileType is not required and will be determined if not given. The documenation for Install-ChocolateyInstallPackage includes in the FileType parameter description:
> If this is not provided, Chocolatey will automatically determine this using the downloaded file's extension.

### Observation:
The FileType parameter definition in the function sets the default value to 'exe':
```powershell
[parameter(Mandatory=$false, Position=1)]
[alias("installerType","installType")][string] $fileType = 'exe',
```
Later, there is code to determine the filetype if it wasn't given:
```powershell
if ($fileType -eq '' -or $fileType -eq $null) {
```
but this will never be true due to the default 'exe' assignment.

Start with the Install-ChocolateyInstallPackage function and compare the FileType parameter default with the later empty-or-null check. Verify the behavior for a local .msi without -filetype, then run the relevant existing tests if available. Done means the documented automatic file-type detection works instead of treating the MSI as an executable.

Written by the indexing model from the issue text.