TASK-115992: New attempted_ip info in ec_message (for logging)

[dkoerichbird]

Note

Introduces documentation for capturing the attempted outbound IP on failed deliveries and exposes it to Lua.

• Adds attempted_ip (since 5.2) to ec_message struct docs; also documents _routing_domain (since 4.3.2)
• Adds new Lua API msg:attempted_ip() reference page and links it in the Lua summary table and index (version 5.2; failure logging phases)
• Minor formatting fix in "See Also" section

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