Enforce a list of available editions in docs pages

[ptgott]

Applies To

Every page in the docs.

Details

We are migrating to a hosted documentation platform that does not support the "Available for" list below the page title banner in our current docs site:

We can indicate which editions a docs page applies to with a standard visual element at the top of each page, for example:

**Available for:** Teleport Enterprise Cloud, Teleport Enterprise

We can enforce the presence of an **Available for** list (and the editions named within the list) using Vale linters.

See the discussion in this PR for context: #38748

How will we know this is resolved?

1. We have added an **Available for** list to each existing docs page. We can use the forScopes field in docs/config.json to automate this.
2. We have added Vale style rules that require an **Available for** list at the top of each page.

Related Issues

[ptgott]

Teleport now has a single commercial edition, "Enterprise", so this move no longer makes sense (see the screenshot from goteleport.com/pricing below). We have also removed the scope icons from the docs engine.