FIX: Gracefully handle DNS issued from SSRF lookup when inline oneboxing (#19631)

There is an issue where chat message processing breaks due to
unhandles `SocketError` exceptions originating in the SSRF check,
specifically in `FinalDestination::Resolver`.

This change gives `FinalDestination::SSRFDetector` a new error class
to wrap the `SocketError` in, and haves the `RetrieveTitle` class
handle that error gracefully.

spec/lib/final_destination/ssrf_detector_spec.rb

@@ -95,6 +95,13 @@ describe FinalDestination::SSRFDetector do
       )
     end
 
+    it "raises an exception if lookup fails" do
+      subject.stubs(:lookup_ips).raises(SocketError)
+      expect { subject.lookup_and_filter_ips("example.com") }.to raise_error(
+        subject::LookupFailedError,
+      )
+    end
+
     it "bypasses filtering for allowlisted hosts" do
       SiteSetting.allowed_internal_hosts = "example.com"
       subject.stubs(:lookup_ips).returns(["127.0.0.1"])