refactor: make message about missing dap clearer

lua/metals/messages.lua

@@ -36,4 +36,8 @@ You have `useGlobalExecutable` set to true, so nvim-metals can't install or
 update your Metals executable. If you'd like nvim-metals to handle this for
 you, remove the `useGlobalExecutable` setting and try again.]]
 
+M.setup_dap_without_nvim_dap = [[
+You can call require("metals").setup_dap() without `nvim-dap` being installed.
+Please make sure `mfussenegger/nvim-dap` is installed.]]
+
 return M

lua/metals/setup.lua

@@ -4,6 +4,7 @@ local lsp = vim.lsp
 local commands_table = require("metals.commands").commands_table
 local conf = require("metals.config")
 local log = require("metals.log")
+local messages = require("metals.messages")
 local util = require("metals.util")
 
 local lsps = {}
@@ -111,13 +112,12 @@ end
 local function setup_dap(execute_command)
   local status, dap = pcall(require, "dap")
   if not status then
-    log.error_and_show("Unable to find nvim-dap. Please make sure mfussenegger/nvim-dap is installed.")
+    log.error_and_show(messages.setup_dap_without_nvim_dap)
     return
   end
 
   dap.adapters.scala = function(callback, config)
     local uri = vim.uri_from_bufnr(0)
-    -- luacheck: ignore
     local arguments = {}
 
     if config.name == "from_lens" then