Convert non-secrets to GitHub environment variables to improve troubleshooting

A number of the values passed to the GitHub workflows as secrets are not actually secrets and should be converted to variables. e.g. TRE_ID is not a secret value and could be a variable.

Converting these to variables would make it easier to verify that all values are present and correct if the deployment fails - this is mostly necessary when deploying a new TRE (especially when using manual auth as it's easy to forget to add a client ID or put the wrong one in).

The only ones that look like they actually should be secrets are:

API_CLIENT_SECRET
APPLICATION_ADMIN_CLIENT_SECRET
TEST_WORKSPACE_APP_SECRET
TEST_ACCOUNT_CLIENT_SECRET
AZURE_CREDENTIALS

Start by locating the GitHub workflow definitions and the deployment configuration that reference the listed values, then compare each current secret with the exceptions identified in the issue. Done means non-secret values such as TRE_ID are exposed as environment variables for troubleshooting, while the five named credentials remain secrets and deployments still receive all required values.