refactor: Move nmap to utils

lua/symbols-outline/utils/init.lua

@@ -1,5 +1,17 @@
 local M = {}
 
+---maps the table|string of keys to the action
+---@param keys table|string
+---@param action string
+function M.nmap(bufnr, keys, action)
+    if type(keys) == 'string' then keys = {keys} end
+
+    for _, value in ipairs(keys) do
+        vim.api.nvim_buf_set_keymap(bufnr, "n", value, action,
+                                    {silent = true, noremap = true})
+    end
+end
+
 --- @param  f function
 --- @param  delay number
 --- @return function