Add JSON path completions for `loadJsonContent` function in Bicep and Bicep Params

**Is your feature request related to a problem? Please describe.**

Sometimes JSON blobs can be large and complex, it would be useful to have completions on the JSON Path, I noticed that the linter already does validation, showing a red squiggly when the path doesn't exist, it would be really convenient to have completions.


**Describe the solution you'd like**
Have the VSCode extension give you JSON path completions

Start by locating the VSCode extension entry point for loadJsonContent in Bicep and Bicep Params, then compare it with the existing linter validation for JSON paths. Done means the extension offers completions for valid paths into JSON blobs in both file types; the issue does not name specific files or tests.

Written by the indexing model from the issue text.