Rewrite the varnish cookbook article
drop varnish 2 example from varnish cookbook article
feature #4627 Rewrite the varnish cookbook article (dbu)

This PR was merged into the 2.3 branch.

Discussion
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Rewrite the varnish cookbook article

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #1505, #4176

Commits
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dc9430a drop varnish 2 example from varnish cookbook article
9ea3671 Rewrite the varnish cookbook article