Restructure with redirects

[aburdenthehand]

Repeating the restructuring work done in #794 which was subsequently rolled back when the redirects did not work as expected.

As in #794, this PR chunks the user guide into smaller sections to aid in navigability. The increased number of section headings does not make change behaviour when viewing on smaller screens.

Lots of file location changes and subsequent xref updates; xref mechanism made consistent and some very old dead urls converted to xrefs. Redirects are all handled in the netlify _redirects file and uses the default 301 permanent redirect code

Edit: I can confirm that the redirects work with the netlify preview. Some examples: https://deploy-preview-801--kubevirt-user-guide.netlify.app/virtual_machines/creating_vms/ https://deploy-preview-801--kubevirt-user-guide.netlify.app/operations/unresponsive_nodes https://deploy-preview-801--kubevirt-user-guide.netlify.app/operations/basic_use

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR. Approvers are expected to review this list.

• [x] Design: A design document was considered and is present (link) or not required
• [x] PR: The PR description is expressive enough and will help future contributors
• [x] Code: Write code that humans can understand and Keep it simple
• [x] Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• [x] Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• [x] Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• [x] Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• [x] Community: Announcement to kubevirt-dev was considered

Release note:

[phoracek]

/approve

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: phoracek

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubevirt/user-guide/blob/main/OWNERS)~~ [phoracek] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[phoracek]

/lgtm

The only thing changed since https://github.com/kubevirt/user-guide/pull/794 was mv _redirects docs/.