feat: toggle sidebar_header (#737)

lua/avante/config.lua

@@ -166,6 +166,7 @@ Respect and use existing conventions, libraries, etc that are already present in
     width = 30, -- default % based on available width in vertical layout
     height = 30, -- default % based on available height in horizontal layout
     sidebar_header = {
+      enabled = true, -- true, false to enable/disable the header
       align = "center", -- left, center, right for title
       rounded = true,
     },

lua/avante/sidebar.lua

@@ -605,6 +605,8 @@ local base_win_options = {
 function Sidebar:render_header(winid, bufnr, header_text, hl, reverse_hl)
   if not bufnr or not api.nvim_buf_is_valid(bufnr) then return end
 
+  if not Config.windows.sidebar_header.enabled then return end
+
   if not Config.windows.sidebar_header.rounded then header_text = " " .. header_text .. " " end
 
   local winbar_text = "%#Normal#"