Deployment Pane: Load Azure Developer CLI environment

With Azure Developer CLI

We have bicep parameter files that read env vars:

```
param environmentName = readFromEnvironmentVariable("AZURE_ENV_NAME")
```

Those values are store in current azd environment.

It would be nice if the deployment pane allowed the user to select the Azure Developer CLI environment they'd like to use.

Which would use azd to load the values needed for the parameters.

Start with the deployment pane and trace how it supplies environment values to Bicep parameter files. Review how Azure Developer CLI environments expose AZURE_ENV_NAME and related values, then define the selection and loading flow. Done means a user can select an azd environment and deploy using its parameter values.

Written by the indexing model from the issue text.