Standardize environment variables

### What problem are you facing?

Functions based on this template are independently setting the environment variables. While this is completely fine, we should aim for standard environment variables, similarly as we do for CLI arguments (think of --tls-certs-dir and `TLS_SERVER_CERTS_DIR`, which many functions share today).

### How could this Function help solve your problem?

All "common" CLI arguments should have an associated env variable.

No files or tests are identified. Start by mapping the common CLI arguments in the template and comparing existing conventions such as --tls-certs-dir and TLS_SERVER_CERTS_DIR; done means every agreed common CLI argument has a corresponding standardized environment variable.

Written by the indexing model from the issue text.