Update guideline ordering and align with public modules

Reordering is mostly based on having all repo-level guidelines together and then dive into the actual content/resources.

This includes addition of repo naming guidelines, more clarification around the expected files, and an update to the sample readme to add type, default, and required values for inputs. Most suggestions reflect what HashiCorp recommends/requires when using public registries. One of the big advantages with consistent naming is easier discoverability, but maybe open the door for us to scan the repos and build our own registry-like site for others to scan (rather than going to GitLab directly).

Reference documents:

• https://www.terraform.io/docs/registry/modules/publish.html#requirements
• https://www.terraform.io/docs/modules/index.html#standard-module-structure