Re-add Neovim configuration files

Re-included from https://github.com/opdavies/opdavies.nvim.

config/neovim/plugin/conform.lua

@@ -0,0 +1,45 @@
+local conform = require "conform"
+
+conform.setup {
+  formatters_by_ft = {
+    bash = { "shellcheck" },
+    javascript = { { "prettierd", "prettier" } },
+    just = { "just" },
+    lua = { "stylua" },
+    nix = { { "nixfmt" } },
+    php = { { "php_cs_fixer", "phpcbf" } },
+    terraform = { "terraform_fmt" },
+    yaml = { "yamlfmt" },
+  },
+
+  format_on_save = function(bufnr)
+    -- Disable with a global or buffer-local variable.
+    if vim.g.disable_autoformat or vim.b[bufnr].disable_autoformat then
+      return
+    end
+
+    return {
+      lsp_fallback = false,
+      quiet = true,
+    }
+  end,
+}
+
+vim.api.nvim_create_user_command("FormatDisable", function(args)
+  if args.bang then
+    -- FormatDisable! will disable formatting just for this buffer
+    vim.b.disable_autoformat = true
+  else
+    vim.g.disable_autoformat = true
+  end
+end, {
+  desc = "Disable autoformat-on-save",
+  bang = true,
+})
+
+vim.api.nvim_create_user_command("FormatEnable", function()
+  vim.b.disable_autoformat = false
+  vim.g.disable_autoformat = false
+end, {
+  desc = "Re-enable autoformat-on-save",
+})