Expand feature-set for interacting with environment variables

[MicroFish91]

Currently we only enable users to add environment variables by importing an .env file. Here are some improvements we should add to enable users....

List of work item ideas, can turn these into their own issues:

• Add view (Add container view to container apps  #673)
• Add addEnvironmentVariable support #784
• Delete environment variable
• Edit environment variable
• Add ability to convert existing environment variable to use container app secrets
• Ensure tree view can display environment variable secretRefs #766
• Explore a solution to use existing environment configuration with deployWorkspaceProject #764