Dev container updates

[brooke-hamilton]

Description

This PR adds the following to the dev container to improve the contributor experience:

• Docker-in-docker configuration, which enables local builds of the dashboard container.
• The current version of Radius, which enables local testing of the dashboard with the current Radius release.
• An environment variable that configures corepack enable to bypass the user prompt in the dev container post create command.
• The Bicep VS Code extension, which helps when testing with Radius.

Type of change

• This pull request is a minor refactor, code cleanup, test improvement, or other maintenance task and doesn't change the functionality of Radius Dashboard (issue link optional).

Fixes: N/A