chore(domainfilter): use pointer receivers for DomainFilter

[u-kai]

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What does it do ?

Standardizes DomainFilter method receivers to use pointer receivers consistently. Changes DomainFilter methods (Match, IsConfigured, MarshalJSON, MatchParent) from value receivers to pointer receivers, and fixes the corresponding json.Marshal call to use &domainFilter.

Motivation

This addresses the discussion in #5522 where inconsistent receiver types were identified in the DomainFilter struct. Since UnmarshalJSON requires a pointer receiver, all other methods should use pointer receivers for consistency. This change prepares the codebase for enabling the recvcheck linter and improves overall code consistency.

More

• [x] Yes, this PR title follows Conventional Commits
• [ ] Yes, I added unit tests
• [ ] Yes, I updated end user documentation accordingly