feat: support multi-line values in metagen (#1514)

Author: benlubas

lua/neorg/modules/core/esupports/metagen/module.lua

@@ -269,10 +269,10 @@ module.public = {
                 -- override with data from metadata table
                 data = { data[1], metadata[data[1]] }
             end
-            table.insert(
-                result,
-                whitespace .. data[1] .. delimiter .. tostring(type(data[2]) == "function" and data[2]() or data[2])
-            )
+            local lines = whitespace .. data[1] .. delimiter .. tostring(type(data[2]) == "function" and data[2]() or data[2])
+            for line in ipairs(vim.split(lines, "\n")) do
+                table.insert(result, line)
+            end
         end
 
         table.insert(result, "@end")