[draft] ICP Dev Docs Restructure, Overhaul & Audit

[jessiemongeon1]

This PR restructures the ICP Dev Docs and makes several significant changes:

• Created new documentation categories and top navigation bar sections.
• Renamed all documentation files to reflect new categories and sections.
• Removed several pages that will be migrated to new ICP Learn Hub website.
• Updated and audited all links across all docs pages, internal and external.
• If a code example used in the docs was originally sourced from the dfinity/examples repo, the code is now referencing the dfinity/examples repo file through a submodule rather than being duplicated in the documentation page.
• If a code example used in the docs is available from an external GitHub repo, it is now embedded into the page directly via GitHub URL.
• Audited every docs page for spelling, grammar, and formatting.
• Applied several style guide revisions for consistency in use of hyphens, terminology, capitalization, etc.
• Increased Docs Sidebar by 50px to better display long titles.
• Fixed bug where single pages rendered as bold text on the sidebar.

[github-actions]

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