AZ CLI DevContainer Feature doesn't install extensions

[damoodamoo]

The json for the devcontainer in the repo doesn't install the extensions specified, and a workaround has to be used to 'manually' install the extension currently.

[martinpeck]

This appears to be due to an interaction between the azure-cli feature and the azure-cli-persistence feature within the dev container.

The azure-cli-persistence feature creates and mounts a volume so that the contents of the .azure folder persist across devcontainer builds. This allows a developer's login to persist, but it also means that extensions installed manually persist.

For now, the work around is:

• remove any reference to installing azcli extensions from the devcontainer.json
• install the required azcli extensions using a postCreate command, and a bash script