feat(formatting): shfmt: use 2-char indents

lua/plugins/formatting.lua

@@ -0,0 +1,9 @@
+return {
+  "stevearc/conform.nvim",
+  opts = {
+    formatters = {
+      -- https://github.com/mvdan/sh/blob/master/cmd/shfmt/shfmt.1.scd#printer-flags
+      shfmt = { prepend_args = { "-i", "2", "-ci", "-bn" } },
+    },
+  },
+}