option to reduce noisy Lua_LS's missing-fields warnings (nvim-lua#511)

(cherry picked from commit ee9790b)

init.lua

@@ -642,6 +642,8 @@ local servers = {
     Lua = {
       workspace = { checkThirdParty = false },
       telemetry = { enable = false },
+      -- NOTE: toggle below to ignore Lua_LS's noisy `missing-fields` warnings
+      -- diagnostics = { disable = { 'missing-fields' } },
     },
   },
 }