praefect/config: Support generating configuration via external command
In 0c21142c (gitaly/config: Support generating configuration via external command, 2023-03-17), we have implemented the ability for Gitaly to read parts of its configuration from an external command. The most important usecase for this functionality is to not store passwords or other secrets on disk, but instead allow the administrator to retrieve them dynamically e.g. via AWS Secrets.
Implement the same functionality for Praefect.
Closes #5076 (closed).
Edited by Patrick Steinhardt