Display Parameter Default Value in Completions

While a big fan of the Bicep Extension for VSCode, I'm missing the feature for it to show a parameter's default in the same way it shows, for example, allowedValues or their structure (in UDTs).

For example, ideally, the popup for the following parameter should show `premium`, yet it doesn't.

One of our AVM contributors, @bryansan-msft, suggested to add the defaultrs to the description in the parameter's metadata which will definitely help. Yet it would mean the default value would need to be maintained both in the actual default value, as well as the description ([ref](https://github.com/Azure/bicep-registry-modules/pull/1223#discussion_r1520165741)).

Having it instead in the parameter's pop-up when using a module's parameter would be an ideal solution.

I was suprised to not find a pre-existing feature request, so here we go.

Start in the Bicep VSCode extension's completion popup behavior and trace how module parameter metadata is presented. Compare the existing allowedValues and UDT structure display with parameter defaults; done means a module parameter completion shows its default value without duplicating it in the description.

Written by the indexing model from the issue text.