Improve UI Definition in managed application example

The Create UI definition for Managed Apps allows more flexibility in the way the UI is displayed. For example, instead of a cryptic sku name we can create an illustrative name, see https://docs.microsoft.com/en-us/azure/managed-applications/microsoft-common-dropdown

We can also use logical functions to hide elements, see https://docs.microsoft.com/en-us/azure/managed-applications/create-uidefinition-functions#logical-functions

So we can, for example, create three groups of SKU dropdowns for postgres, mysql and mssql and only have them display when the appropriate DB is selected.

Locate the managed application example and inspect its current UI definition. Read the linked Microsoft documentation on common dropdowns and logical functions, then update the example so SKU names are illustrative and PostgreSQL, MySQL, and MSSQL SKU groups appear conditionally for the selected database.

Written by the indexing model from the issue text.