🏃Fix all 404s in book and add a verify script to ensure there are no 404s

[chuckha]

What this PR does / why we need it:
This PR adds to the verify make target that checks the book for 404s.

In addition this fixes all 404s in the book.

This introduces this as a tool: https://github.com/raviqqe/liche which is used by the knative team to check for 404s in their book.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chuckha

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 [chuckha]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[vincepri]

/milestone v0.3.0-rc.3

[k8s-ci-robot]

@chuckha: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-cluster-api-capd-e2e	72ebca7	link	/test pull-cluster-api-capd-e2e

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[vincepri]

/lgtm