Allow for short titles for sidebar

[shainaraskas]

Longer titles have SEO value and make the scope of the page clear, but in the sidebar, they add mess, especially when they're repetitive

The ask: allow for some method to define a short title that will be used in the sidebar

[bmorelli25]

We have this! And I can definitely improve the existing docs: https://elastic.github.io/docs-builder/syntax/titles.html.

tl;dr: Add frontmatter:

---
navigation_title: Short title for nav
---

# Long, SEO friendly title

[shainaraskas]

yeah, I read that page and just :whoosh:ed right over that. thanks @bmorelli25 !!!