Adds 'list all files with missing required metadata' sample. Closes pnp#3277

Author: nicodecleyre

docs/docs/sample-scripts/spo/list-all-files-with-missing-required-metadata/assets/preview.png

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+[
+  {
+    "name": "pnp-list-all-files-with-missing-required-metadata",
+    "source": "pnp",
+    "title": "List all files with missing required metadata",
+    "url": "https://pnp.github.io/cli-microsoft365/sample-scripts/spo/list-all-files-with-missing-required-metadata",
+    "creationDateTime": "2022-12-31",
+    "updateDateTime": "2022-12-31",
+    "shortDescription": "List all files with missing required metadata.",
+    "longDescription": [
+      "List all files with missing required metadata."
+    ],
+    "products": [
+      "SharePoint"
+    ],
+    "categories": [],
+    "tags": [
+      "files",
+      "reports"
+    ],
+    "metadata": [
+      {
+        "key": "CLI-FOR-MICROSOFT365",
+        "value": "6.0.0"
+      }
+    ],
+    "thumbnails": [
+      {
+        "type": "image",
+        "order": 100,
+        "url": "https://raw.githubusercontent.com/pnp/cli-microsoft365/main/docs/docs/sample-scripts/spo/list-all-files-with-missing-required-metadata/assets/preview.png",
+        "alt": "preview image for the sample"
+      }
+    ],
+    "authors": [
+      {
+        "gitHubAccount": "nicodecleyre",
+        "pictureUrl": "https://avatars.githubusercontent.com/u/35696168?v=4",
+        "name": "Nico De Cleyre"
+      }
+    ],
+    "references": [
+      {
+        "name": "Want to learn more about CLI for Microsoft 365 and the commands",
+        "description": "Check out the CLI for Microsoft 365 site to get started and for the reference to the commands.",
+        "url": "https://aka.ms/cli-m365"
+      }
+    ]
+  }
+]

docs/docs/sample-scripts/spo/list-all-files-with-missing-required-metadata/assets/sample.json

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+---
+tags:
+  - files
+  - reports
+---
+
+# List all files with missing required metadata
+
+Author: [Nico De Cleyre](https://www.nicodecleyre.com), Inspired by [Veronique Lengelle](https://veronicageek.com/2021/find-missing-metadata-using-powershell/)
+
+The following script iterates through all files in all the document libraries of a SharePoint Online site. It returns all the files that have missing required metadata and excludes the `name` metadata
+
+=== "PowerShell"
+
+    ```powershell
+    $siteUrl = "https://<TENANT-NAME>.sharepoint.com/sites/<YOUR-SITE>"
+    $allLists = m365 spo list list --webUrl $($siteURL) --output json | ConvertFrom-Json
+    $allLibs = $allLists | where {$_.BaseTemplate -eq 101}
+    $results = @()
+    $fields = @('FileLeafRef', 'FileSystemObjectType')
+
+    foreach ($lib in $allLibs) {
+        $allRequiredFields = m365 spo field list --webUrl $($siteURL) --listId $($lib.Id) --query "[?Required == ``true``]" --output json | ConvertFrom-Json
+
+        if($allRequiredFields.Length -eq 0){
+            continue
+        }
+
+        [array]$allRequiredFieldsInternalName = $($allRequiredFields | select InternalName).InternalName
+
+        ForEach ($field in $fields)
+        {
+            If (-not ($allRequiredFieldsInternalName -contains $field))
+            {
+                $allRequiredFieldsInternalName += $field
+            }
+        }
+
+        $allItems = m365 spo listitem list --webUrl $($siteURL) --listId $($lib.Id) --fields $($allRequiredFieldsInternalName -join ",") --output json | ConvertFrom-Json
+        $allItems = $allItems | where {$_.FileSystemObjectType -eq 0}
+        
+        foreach($item in $allItems){
+            foreach($requiredfield in $allRequiredFields){
+                if($requiredfield.InternalName -eq "FileLeafRef"){
+                    continue
+                }
+
+                if ($null -eq $item["$($requiredfield.InternalName)"]) {
+                        $results += [pscustomobject]@{
+                            FileName = $item.FileLeafRef
+                            FieldName = $requiredfield.Title
+                            ListOrLibrary = $lib.Title
+                            FileLocation = $lib.RootFolder.ServerRelativeUrl
+                        }
+                }
+            }
+        }
+    }
+    $results
+    ```