Use example.com in WAF policy docs

[alan747271363-art]

Summary

• replace a WAF policy documentation example domain that may resolve to unsafe content
• use the reserved example.com domain for both the domain and sub-URL examples

Closes #2002

Validation

• rg -n "mywebsite\.com|www\.example\.com" content/includes/waf/policy.html
• git diff --check

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[mjang]

@alan747271363-art I'm closing this as it looks like you have other contributions (to other projects) that was identified as "AI Generated"

If you have evidence otherwise, ping me (@mjang ) and present your case.

We want to preserve "Good first contributor" issues for true "first contributors"