content: Complete v0.153.0 updates

[jmooring]

Concept page:

• Create a concept page under "content management" (for now) that digs into the multi-dimensional content model. This should be the starting point for users, pulling together concepts, definitions, related methods, examples, etc. See https://discourse.gohugo.io/t/56516.

Glossary entries:

• Improve sites matrix
• Improve sites complements (see https://discourse.gohugo.io/t/56516/9)

Front matter:

• Improve sites. Maybe move this example to the concept page.

Other tasks:

• Glob negation (create our own reference page instead of linking externally)
• Build order (not sure where to put this, or if it is even important)
• Deprecations (lang option on mounts and segments)

Style guide updates:

• Look at how we use the terms "sites matrix" and "sites complements". Using two words to name a thing can be tricky, because "sites" and "matrix" have meaning on their own. Figure out the best way to reference these things without capitalizing them. Maybe preceding with an article is sufficient, e.g., "When defining a sites matrix be sure to...". Singular and plural get tricky too: "sites matrix" vs "sites matrices" vs "site matrix" vs "site matrices". When thinking about this, remember that "matrix" and "complements" are keys under "sites"...

  sites:
    matrix:
      languages: 
      roles:
      versions:
    complements:
      languages:
      roles:
      versions:

• Tied closely to this is the concept/syntax of "glob", "glob slices", negation, and "dimensional queries".

Reference: #3116