AstroNvim v5 (#29)

* fix(astrocore): update to the new `diagnostics` settings style

* fix(mason): move to installing Mason packages with `mason-tool-installer.nvim`

* fix(user): update dashboard header example to use `snacks.dashboard`

* fix(lazy_setup): bump version to v5 for release

lua/lazy_setup.lua

@@ -1,7 +1,7 @@
 require("lazy").setup({
   {
     "AstroNvim/AstroNvim",
-    version = "^4", -- Remove version tracking to elect for nightly AstroNvim
+    version = "^5", -- Remove version tracking to elect for nightly AstroNvim
     import = "astronvim.plugins",
     opts = { -- AstroNvim options must be set here with the `import` key
       mapleader = " ", -- This ensures the leader key must be configured before Lazy is set up