We are building an ArcGIS Pro add-in with the ArcGIS Pro SDK. What's a good strategy to support older versions of ArcGIS Pro, especially versions using different .NET runtimes? For example, if we are building our next release with the ArcGIS Pro SDK 3.6, how should we support users running ArcGIS Pro 3.5 and older, or even ArcGIS Pro 2.x?