Fix the config and add C# lsp

lua/plugins/roslyn.lua

@@ -0,0 +1,9 @@
+return {
+    "seblyng/roslyn.nvim",
+    ---@module 'roslyn.config'
+    ---@type RoslynNvimConfig
+    opts = {
+        -- your configuration comes here; leave empty for default settings
+    },
+    ft = "cs"
+}