fix: improve domain expiry warning message for unsupported TLDs

[AKIB473]

Summary

In this pull request, the following changes are made:

• The log warning for unsupported TLDs in domain expiry monitoring is improved to give users a clearer explanation and actionable guidance.

• Relates to Clarify domain expiry warning for unsupported TLDs yet more #7190

Problem

The existing warning message:

Domain expiry unsupported for '.de' because its RDAP endpoint is not listed in the IANA database.

Left users confused. Popular TLDs like .de and .eu not supporting RDAP is counterintuitive, and the message gave no guidance on what to do next.

Solution

The new message:

Domain expiry monitoring is not supported for '.de' TLD — no RDAP endpoint is registered for it in the IANA database. Please verify this domain's expiry date manually via your registrar or https://lookup.icann.org.

Changes:

• Clarifies it is a TLD-level limitation, not a configuration error
• Explains why (no RDAP endpoint registered)
• Directs users to verify manually via their registrar or ICANN lookup

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• ⚠️ If there are Breaking change (a fix or feature that alters existing functionality in a way that could cause issues) I have called them out
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