Shipped proxy configs now read general_settings.master_key from
os.environ/LITELLM_MASTER_KEY, the .env examples ship a blank value with
the openssl generate command above it, and READMEs, the missing env vars
page and Admin UI code snippets show a generate command or the
<your-master-key> placeholder instead of the literal sk-1234
The two CircleCI docker runs that mount proxy_server_config.yaml and
oai_misc_config.yaml now pass LITELLM_MASTER_KEY so their runtime key is
unchanged
