Fix sv config files of services to use explicitly passed parameters

Towards #2804 (closed)

Closes #4072

To test runit_service custom resource using a matcher, we need to confirm the correct parameters are passed into the template. This is not possible if we directly use node attributes in the config files. This MR fixes that, and passes each variable needed by the template explicitly to it.

While I was at it, I also tried to bring consistency to the different variables used (user v/s username, group v/s groupname, env_dir v/s environment etc) in different config files.

PS: Individual commits only for easier review. While merging, will be squashed.