[Issue] PageCache/AccessList: Add CIDR support

[m2-assistant]

This issue is automatically created based on existing pull request: #37809: PageCache/AccessList: Add CIDR support

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Description (*)

When accepting purge requests within a network, it's easier to just supply a CIDR range.

Related Pull Requests

None.

Fixed Issues (if relevant)

None.

Manual testing scenarios (*)

1. Go to Advanced -> System -> Full Page Cache -> Varnish Configuration
2. Configure a CIDR range like 172.16.0.1/24
3. Value should be valid and saved

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)