docs: move minimum reproduction template from wiki to repo

Instead of a markdown file, just use a lua file instead that users can
use directly.

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -25,7 +25,7 @@ body:
       description: |
         - For build failures: list the exact steps including CMake flags (if any).
         - For startup or shell-related problems: try `env -i TERM=ansi-256color "$(which nvim)"`.
-        - See [Minimal-reproduction-template](https://github.com/neovim/neovim/wiki/Minimal-reproduction-template) for how to create a minimal configuration.
+        - Use the provided [minimal reproduction template](https://github.com/neovim/neovim/blob/master/contrib/minimal.lua) to create a minimal configuration. After you fill it out with necessary information, run with `nvim --clean -u minimal.lua`.
         - Please do **not** include a package manager in the reproduction steps.
       placeholder: |
         nvim --clean

CONTRIBUTING.md

@@ -21,6 +21,7 @@ Reporting problems
 - [Search existing issues][github-issues] (including closed!)
 - Update Neovim to the latest version to see if your problem persists.
 - Try to reproduce with `nvim --clean` ("factory defaults").
+- If a specific configuration or plugin is necessary to recreate the problem, use the minimal template in `contrib/minimal.lua` with `nvim --clean -u contrib/minimal.lua` after making the necessary changes.
 - [Bisect](https://neovim.io/doc/user/starting.html#bisect) your config: disable plugins incrementally, to narrow down the cause of the issue.
 - [Bisect][git-bisect] Neovim's source code to find the cause of a regression, if you can. This is _extremely_ helpful.
 - When reporting a crash, [include a stacktrace](https://github.com/neovim/neovim/wiki/FAQ#backtrace-linux).

contrib/minimal.lua

@@ -0,0 +1,14 @@
+-- Run this file as `nvim --clean -u minimal.lua`
+
+for name, url in pairs{
+  -- ADD PLUGINS _NECESSARY_ TO REPRODUCE THE ISSUE, e.g:
+  -- some_plugin = 'https://github.com/author/plugin.nvim'
+} do
+  local install_path = vim.fn.fnamemodify('nvim_issue/'..name, ':p')
+  if vim.fn.isdirectory(install_path) == 0 then
+    vim.fn.system { 'git', 'clone', '--depth=1', url, install_path }
+  end
+  vim.opt.runtimepath:append(install_path)
+end
+
+-- ADD INIT.LUA SETTINGS _NECESSARY_ FOR REPRODUCING THE ISSUE