fix(rust): update rustaceanvim docs to use AstroLSP settings

Author: mehalter

src/content/docs/recipes/advanced_lsp.mdx

@@ -587,6 +587,28 @@ return {
     'mrcjkb/rustaceanvim', -- add lsp plugin
     version = '^5',
     lazy = false, -- This plugin is already lazy
+    opts = function(_, opts)
+      local astrolsp_avail, astrolsp = pcall(require, "astrolsp")
+      local astrolsp_opts = (astrolsp_avail and astrolsp.lsp_opts "rust_analyzer") or {}
+      local server = {
+        ---@type table | (fun(project_root:string|nil, default_settings: table|nil):table) -- The rust-analyzer settings or a function that creates them.
+        settings = function(project_root, default_settings)
+          local astrolsp_settings = astrolsp_opts.settings or {}
+
+          local merge_table = require("astrocore").extend_tbl(default_settings or {}, astrolsp_settings)
+          local ra = require "rustaceanvim.config.server"
+          -- load_rust_analyzer_settings merges any found settings with the passed in default settings table and then returns that table
+          return ra.load_rust_analyzer_settings(project_root, {
+            settings_file_pattern = "rust-analyzer.json",
+            default_settings = merge_table,
+          })
+        end,
+      }
+      return { server = require("astrocore").extend_tbl(astrolsp_opts, server) }
+    end,
+    -- configure `rustaceanvim` by setting the `vim.g.rustaceanvim` variable
+    config = function(_, opts) vim.g.rustaceanvim = require("astrocore").extend_tbl(opts, vim.g.rustaceanvim) end,
+
   },
   {
     "AstroNvim/astrolsp",