Render schemas in a documentation-friendly form

[mreid-moz]

Using something like this would let us render the schemas in a readable way, which would potentially avoid the need for manually created docs like the "structure" part of these in-tree ones for the main ping.

[mreid-moz]

cc @dblohm7

[acmiyaguchi]

Another alternative is bundling in a custom solution like https://github.com/mozilla/schema-dictionary, although this will likely be replaced by https://github.com/mozilla/glean-dictionary.