Update docs summary

[willie-yao]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
This PR fixes the ordering of topics in SUMMARY.md and adds a link to the ClusterClass docs.

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:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

[CecileRobertMichon]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: d1d036640683e9ece2411865fbab1969d3b1f3e0

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

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Needs approval from an approver in each of these files:

• OWNERS [CecileRobertMichon]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (55e0559) 59.55% compared to head (389b6bc) 59.72%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4288      +/-   ##
==========================================
+ Coverage   59.55%   59.72%   +0.16%     
==========================================
  Files         185      192       +7     
  Lines       18782    19303     +521     
==========================================
+ Hits        11186    11529     +343     
- Misses       6981     7144     +163     
- Partials      615      630      +15     

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[willie-yao]

/cherry-pick release-1.12

[k8s-infra-cherrypick-robot]

@willie-yao: new pull request created: #4378

In response to this:

/cherry-pick release-1.12

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