ci: add file linting for size and name

[ghostrider-05]

Please describe the changes this PR makes and why it should be merged:

NOTE: updates the contributing guidelines to be stricter

• adds npm run lint-files:name to validate the new guidelines for naming files
• adds npm run lint-files:size to validate files to be < 1MB
• adds an action to label PRs on file changes
• adds a step in the build process to validate frontmatter (keys)

Code changes:

• updates eslint to v9
• pins theme-rlmm to github releases
• updates theme-rlmm to v0.7.0 and enables the steam maps title switcher on the home page
• refactors configuration code

Guide changes:

• typos fixed and some headers updated
• updates all images to have meaningful file names and alt texts
• adds the page-inline-images class to display all images inline on a page
• add GitHub link to guide contributers
• adds back the Mipmaps and LOD page in the sidebar
• rename The owl page to Building a map
• adds features to testing and building page
  
  

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Documentation changes
• Build-related changes
• Other, please describe:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• Code changes have been tested locally, or there are no code changes
• I have followed the steps to contribute and followed the guidelines
• If my contribution contains a workflow, I've performed said workflow directly before making the change request and no steps are missing.

Other information