feat(renderer): add renderer.indent_width (#1505)

* feat: add config option for a tree indent width

add 'indent_width' option to configure visible indent for tree nesting
levels (default is 2).

* add 'bottom' char for a corner extension

* apply stylua formatting

* provide value constraints in documentation

* limit minimal indent width

* make marker symbols have one utf8 char width

* match stylua formatting

* add the commentary regarding utf-8 first symbol match

lua/nvim-tree.lua

@@ -476,6 +476,7 @@ local DEFAULT_OPTS = { -- BEGIN_DEFAULT_OPTS
     full_name = false,
     highlight_opened_files = "none",
     root_folder_modifier = ":~",
+    indent_width = 2,
     indent_markers = {
       enable = false,
       inline_arrows = true,
@@ -483,6 +484,7 @@ local DEFAULT_OPTS = { -- BEGIN_DEFAULT_OPTS
         corner = "└",
         edge = "│",
         item = "│",
+        bottom = "─",
         none = " ",
       },
     },