feat: optionally append BA credentials to URL destinations

• If BA credentials are present in standardized service config file, append them to the CURL command like '-u user:pass'.
• Supported in generic_send.py and generic_sender.py scripts when everything runs the standard way. If you override transport_command or create it by using generic_sender.prepare_url_transport_command() then no credentials are appended, and you have to do it by yourself.
• We can't simply use overridden transport_command for this functionality, since it doesn't work for URL destinations correctly (can't catch stdout in temporary file).

DEPLOYMENT NOTE:

• All services using URL destination and standard send script will start append basic auth credentials if stored in their config at /etc/perun/services/service_name/service_name.py
• Locally modified send scripts need to be checked and updated.
• Configuration for pithia_portal service must be updated to not use default properties for authentication to token endpoint (username -> tokenUsername, password -> tokenPassword).