Address clippy fixes in the generated documentation

[suryapandian]

1. The document generated should have backticks
   For example:
   Current behavior: /// RuleGroup is a list of sequentially evaluated
   Expected behavior: /// RuleGroup is a list of sequentially evaluated

2. Bare URLs should be between </> or should be made a proper Markdown links
   Current behavior: More info: https://github.com/thanos-io/thanos/blob/main/docs/components/rule.md#partial-response
   Expected behavior More info
   or /https://github.com/thanos-io/thanos/blob/main/docs/components/rule.md#partial-response/

For more info:
https://rust-lang.github.io/rust-clippy/master/index.html#doc_markdown

[clux]

For 1; It is possible to build up a list of all symbols we see and auto-backtick them in docs before printing whenever we see them. Could be a nice optional feature, but note that we can never fix all the cases because it's impossible to know if they are referring to types outside the schema.

For 2 We'd have to just wrap the link. Could be an escaping function - provided there's a standard way to identify urls.

PRs welcome around src/output.rs here.