perf(supermaven): add lazy-loading (#5183)

## Description

As title, somehow these events have been forgotten, ive checked the git
history of it aswell.

## Related Issue(s)

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  - Fixes #<issue_number>
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## Screenshots

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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/ai/supermaven.lua

@@ -1,6 +1,11 @@
 return {
   {
     "supermaven-inc/supermaven-nvim",
+    event = "InsertEnter",
+    cmd = {
+      "SupermavenUseFree",
+      "SupermavenUsePro",
+    },
     opts = {
       keymaps = {
         accept_suggestion = nil, -- handled by nvim-cmp / blink.cmp