Restructure content to better present three orb options, URL, inline and registry

[rosieyohannan]

• Archive old create and orb page in favour of three pages for creating: Inline, URL, registry orbs.
• Various updates to cross references due to archival and moving the orbs concepts page the the "Use" module from "Author".
• Add section for comparing the different orb types to help people decide which to make for their use case.
• More clearly signpost when content is for a specific orb type and to lay out clearly that there are different orb types.
• Clear up navigation, remove "reference" section
• Add how to section to managing URL orb allow list page to help people understand how to create their allow list entries (https://circleci.atlassian.net/browse/DOCSS-1797)