feat(file_selector): add intergration with nvim-tree.lua (#1987)

Co-authored-by: doodleEsc <cokie@foxmail.com>
Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

lua/avante/extensions/init.lua

@@ -0,0 +1,10 @@
+---@class avante.extensions
+local M = {}
+
+setmetatable(M, {
+  __index = function(t, k)
+    ---@diagnostic disable-next-line: no-unknown
+    t[k] = require("avante.extensions." .. k)
+    return t[k]
+  end,
+})