feat(lang): add markdown support (#1718)

* feat(lang): add markdown support

* feat: use peek.nvim instead of markdown-preview. Disable and show warning when deno is not installed

* feat: add markdown-preview back

---------

Co-authored-by: Folke Lemaitre <folke.lemaitre@gmail.com>

lua/lazyvim/plugins/extras/lang/markdown.lua

@@ -0,0 +1,64 @@
+return {
+  {
+    "nvim-treesitter/nvim-treesitter",
+    opts = function(_, opts)
+      if type(opts.ensure_installed) == "table" then
+        vim.list_extend(opts.ensure_installed, { "markdown", "markdown_inline" })
+      end
+    end,
+  },
+  {
+    "williamboman/mason.nvim",
+    opts = function(_, opts)
+      opts.ensure_installed = opts.ensure_installed or {}
+      vim.list_extend(opts.ensure_installed, { "markdownlint" })
+    end,
+  },
+  {
+    "nvimtools/none-ls.nvim",
+    optional = true,
+    opts = function(_, opts)
+      local nls = require("null-ls")
+      opts.sources = vim.list_extend(opts.sources or {}, {
+        nls.builtins.diagnostics.markdownlint,
+      })
+    end,
+  },
+  {
+    "mfussenegger/nvim-lint",
+    optional = true,
+    opts = {
+      linters_by_ft = {
+        markdown = { "markdownlint" },
+      },
+    },
+  },
+  {
+    "neovim/nvim-lspconfig",
+    opts = {
+      servers = {
+        marksman = {},
+      },
+    },
+  },
+
+  -- Markdown preview
+  {
+    "iamcco/markdown-preview.nvim",
+    cmd = { "MarkdownPreviewToggle", "MarkdownPreview", "MarkdownPreviewStop" },
+    build = function()
+      vim.fn["mkdp#util#install"]()
+    end,
+    keys = {
+      {
+        "<leader>cp",
+        ft = "markdown",
+        "<cmd>MarkdownPreviewToggle<cr>",
+        desc = "Peek (Markdown Preview)",
+      },
+    },
+    config = function()
+      vim.cmd([[do FileType]])
+    end,
+  },
+}