add function for getting joined rooms

public/Get-MatrixJoinedRooms.ps1

@@ -0,0 +1,52 @@
+function Get-MatrixJoinedRooms {
+    param(
+        [Parameter(Mandatory)]
+        [string]$ServerUrl,
+
+        [Parameter(Mandatory)]
+        [SecureString]$AccessToken
+    )
+
+    try {
+        $url = New-MatrixUrl -ServerUrl $ServerUrl -ApiPath "_matrix/client/v3/joined_rooms"
+    }
+    catch {
+        Write-Error $Error[0]
+        return
+    }
+
+    $headers = Get-MatrixAuthHeaders -AccessToken $AccessToken
+
+    $res = Invoke-RestMethod -Uri $url -Headers $headers
+    $rooms = @()
+
+    foreach($roomId in $res.joined_rooms) {
+        $roomAliasUrl = New-MatrixUrl -ServerUrl $ServerUrl -ApiPath "_matrix/client/v3/rooms/$roomId/state/m.room.canonical_alias"
+        $mainAlias = $null
+        $altAliases = @()
+
+        Write-Debug "Retrieving aliases for room ID $roomId via request $roomAliasUrl"
+
+        try {
+            $aliasRes = Invoke-RestMethod -Uri $roomAliasUrl -Headers $headers
+            $mainAlias = $aliasRes.alias
+            $altAliases = $aliasRes.alt_aliases
+            if($null -eq $altAliases) {
+                $altAliases = @()
+            }
+        }
+        catch {
+            # Write-Warning $Error[0]
+        }
+
+        $room = [PSCustomObject]@{
+            RoomID = $roomId
+            MainAlias = $mainAlias
+            AltAliases = $altAliases
+        }
+
+        $rooms += $room
+    }
+
+    return $rooms
+}