add Join-MatrixRoom function

public/Join-MatrixRoom.ps1

@@ -0,0 +1,23 @@
+function Join-MatrixRoom {
+    param(
+        [Parameter(Mandatory)]
+        [string]$ServerUrl,
+
+        [Parameter(Mandatory)]
+        [SecureString]$AccessToken,
+
+        [Parameter(Mandatory)]
+        [string]$RoomAliasOrId
+    )
+
+    $url = New-MatrixUrl -ServerUrl $ServerUrl -ApiPath "_matrix/client/v3/join/$RoomAliasOrId?server_name=techlore.net"
+    $headers = Get-MatrixAuthHeaders -AccessToken $AccessToken
+    $method = "POST"
+    
+    try {
+        $res = Invoke-RestMethod -Uri $url -Headers $headers -Method $method
+        return $res
+    } catch {
+        Write-Error $_
+    }
+}