The Bicep Language Server should provide completions for import 'az@ by inspection of the OCI registry

## Overview

With the introduction of dynamic type loading we want the user experience in VSCode to change so that it gives package completions to the authors of a bicep file.

For example: When the author is typing the below trivia statement, the language server should provide intellisense about what are the available versions of the `az` provider at the time by querying the OCI registry. Likely it would be also nice to have a documentation string as part of the intellisense prompt telling the user what date the provider was released so we have a hint of what types are available in that provider version

```bicep
import 'az@
```

Start by locating the Bicep language-server completion entry point for import statements and the existing dynamic type-loading or OCI registry path. Define completion behavior for available az provider versions and the release-date documentation shown in IntelliSense. Done means typing `import 'az@` offers registry-backed versions with the expected documentation.

Written by the indexing model from the issue text.