docs(role): Docs for lgsm

[heihachi]

Create documentation for how to setup the lgsm role. Mostly how to properly setup the inventory settings and where all the configs are located.

• [ ] App documentation page created
• [x] markdownlint reports no errors on edited page(s) - use https://dlaa.me/markdownlint/ if your IDE does not have this built in
• [x] Reference added in docs/sandbox/index.md
• [x] Reference added in mkdocs.yml nav menu

Do I need the previewing setup for App documentation page created I just used markdown previewers to see how it was generated.