[Installation] - Improve Installation for Windows Users

- **What this feature does**:
Windows user should be able to use the dagger binary getting a similar experience to the one proposed for Linux in the docs.
- **What has been changed**: the feature implement a powershell script similar to `install.sh` logic. More specifically I've updated `install.md` and added `install.ps1`

I'm not sure if the  URL `releases.dagger.io` is currently pointing at the content of GH repo or something else so the documented steps may need a review.

Signed-off-by: alefesta <afesta@alfweb.com>

docs/install.md

@@ -35,6 +35,23 @@ You can then install it globally on your system:
 sudo mv ./bin/dagger /usr/local/bin
 ```
 
+## Option 2 (Windows): Run a shell script
+
+Since Dagger repository is currently private, we have to use a workaround
+to be able to run the script and match the latest release.
+This workaround will be removed once the repo will become public.
+To generate a personal access token on GitHub follow the guidelines  at [Create a personal access token](https://docs.github.com/en/github/authenticating-to-github/keeping-your-account-and-data-secure/creating-a-personal-access-token)
+
+From a terminal, run the following command:
+
+```shell
+$personalToken= <INSERT YOUR PERSONAL TOKEN>
+curl https://releases.dagger.io/dagger/install.ps1 -OutFile install.ps1 ; ./install.ps1 -PersonalToken $personalToken; rm install.ps1
+```
+
+We try to move the dagger binary under `C:\Windows\System32` but
+in case use missing the necessary permission we'll save everything under `<your home folder>/dagger`
+
 ## Option 3: Download a binary release
 
 Open your web browser to [the latest release](https://github.com/dagger/dagger/releases/latest).

install.ps1

@@ -0,0 +1,82 @@
+param (
+    [Parameter(Mandatory)] $PersonalToken  
+)
+Clear-Host
+@"
+
+---------------------------------------------------------------------------------
+Author: Alessandro Festa
+Usage: To run using your GH personal developer token simply use the flag as below
+./install.ps1 -PersonalToken 1234567891213
+Dagger executable will be save under the folder "dagger" in your home folder.
+---------------------------------------------------------------------------------
+
+"@
+
+# Since we are already authenticated we may directly download latest version.
+$name="dagger"
+$base="https://dagger-io.s3.amazonaws.com"
+function http_download {
+    Clear-Host
+    $version=Get_Version
+    $version= $version -replace '[""]'
+    $url = $base + "/" + $name + "/releases/" + $version.substring(1) + "/dagger_" + $version + "_windows_amd64.zip"
+    $fileName="dagger_" + $version + "_windows_amd64"
+    
+
+    Invoke-WebRequest -Uri $url -OutFile $env:temp/$fileName.zip -ErrorAction Stop
+    Expand-Archive -Path $env:temp/$fileName.zip -DestinationPath $env:HOMEPATH/dagger -Force -ErrorVariable ProcessError;
+    If ($ProcessError)
+    {
+    Clear-Host
+@"
+Whoops apparently we had an issue in unzipping the file, please check
+you have the right permission to do so and try to unzip manually the file.
+Currently we saved Dagger at your temp folder.
+"@
+exit
+    } else {
+        Clear-Host
+    
+@"
+
+Thank You for downloading Dagger!
+
+-----------------------------------------------------
+Dagger has been saved at <YOUR HOME FOLDER>/dagger/
+Please add dagger.exe to your PATH in order to use it
+----------------------------------------------------
+
+"@
+    }
+
+}
+
+function Get_Version {
+
+    $headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
+    $headers.Add("Authorization", "token $PersonalToken")
+    $headers.Add("Accept", "application/vnd.github.VERSION.raw")
+    
+    $response = Invoke-RestMethod 'https://api.github.com/repos/dagger/dagger/releases/latest' -Method 'GET' -Headers $headers -Body $body -ErrorAction SilentlyContinue -ErrorVariable DownloadError
+    If ($DownloadError)
+    {
+    Clear-Host
+@"
+
+---------------------------------------------------------------------------
+Houston we have a problem!
+
+Apparently we had an issue in downloading the file, please try again
+run the script and if it still fail please open an issue on the Dagger repo.
+----------------------------------------------------------------------------
+
+"@
+exit
+    }
+    
+    return $response.tag_name| ConvertTo-Json
+    
+}
+
+http_download