chore(api-references/rest): add keywords
fix(nagivated-docs): add debounce on search

Related to CAM-1120
Merge branch 'master' of github.com:camunda/docs.camunda.org
feat(docs/single-page): add single page document

New layout 'single-page' may be used to create a single page document
from a group of documentation parts.

The site including the layout must specify the parts via its meta data.

Example:

---

chapters:
    - title: 'REST API'
      part: 'api-references/rest'

    - title: 'User Guide'
      part: 'guides/user-guide'

---

Closes CAM-1265