Closes https://github.com/elastic/docs-content-internal/issues/55

Restructures and adds to the docs on how to write cumulative documentation.

I started collecting examples from across Slack and GitHub where the Docs team has been discussing how we should approach cumulative documentation in different scenarios. This will add a best practices doc outlining what I've found. There are some situations where I've found conflicting or incomplete advice. In those cases, I'll try to get consensus. 🙃

Approach

Splits content on writing cumulative documentation into several pages with different goals and/or audiences based on conversations I've had over the last couple months with dev teams, other writers, and other docs contributors:

• Intro to cumulative documentation:
  • Audience: Anyone who is curious about the cumulative documentation model whether or not they contribute to docs regularly (or at all).
  • Goals:
    • Introduce the concept of cumulative documentation.
    • Explain its impacts on both readers and contributors.
    • Point docs contributors to more detailed resources on how to write cumulative documentation.
• Guidelines:
  • Audience: Anyone who contributes to docs.
  • Goals:
    • Provide general guidance that is appropriate for both experienced and new docs contributors.
    • Point docs contributors to specific examples as needed without distracting from general guidance.
• Badge placement:
  • Audience: Technical writers and other frequent docs contributors.
  • Goals:
    • Provide guidance on badge placement in specific situations to promote consistency.
• Example scenarios:
  • Audience: Technical writers and other frequent docs contributors.
  • Goals:
    • Provide realistic, detailed examples of common scenarios docs contributors will run into.
    • Help docs contributors choose the best solution.
• Quick reference:
  • Audience: Anyone who contributes to docs.
  • Goals:
    • Make it easier for those who are already familiar with applies_to to find the list of valid values without having to dig through all the information in Syntax > Applies to.

I also moved the content in Versions and types closer to the docs on cumulative documentation.

For reviewers

Where there was conflicting guidance in GitHub/Slack or docs contributors used inconsistent strategies across the live docs, I tried to make a judgement call. If you you disagree or have another approach we should consider, feedback/input is very welcome! I tried to highlight some of the spiciest takes 🌶️ with a code comment: % FOR THE REVIEWER.

My focus in this PR is to capture the nuances of cumulative documentation and providing guidance on as many scenarios as possible. I haven't had a chance to reread the content for copy editing purposes. If anyone wants to do an editing pass they are welcome to edit and commit changes directly instead of adding MANY suggestions.