Creating the log analytics workspace first and then providing the workspace ID and workspace key at container group creation worked fine for me (no need to create them both "at the same time"). Note, that it does take up to 10 minutes (according to the docs) for the ContainerInstanceLog_CL
table to populate with your container's console logs.
Various programmatic ways to specify this at container creation, pertinent bit of C# client code shown below.
var containerGroupData = new ContainerGroupData(location, new[] { container }, ContainerInstanceOperatingSystemType.Linux);
var logAnalyticsWorkspaceId = ConfigurationManager.AppSettings["LogAnalyticsWorkspaceId"];
var logAnalyticsWorkspaceKey = ConfigurationManager.AppSettings["LogAnalyticsWorkspaceKey"];
containerGroupData.DiagnosticsLogAnalytics = new ContainerGroupLogAnalytics(logAnalyticsWorkspaceId, logAnalyticsWorkspaceKey);