Make all plugin configs return a function

Simplifies writing the `config = ...` field for each plugin

lua/plugins/treesitter-context.lua

@@ -16,7 +16,11 @@
 
 -- https://github.com/nvim-treesitter/nvim-treesitter-context
 
-require("treesitter-context").setup({
-    max_lines = 1,
-    min_window_height = 10,
-})
+local function setup()
+    require("treesitter-context").setup({
+        max_lines = 1,
+        min_window_height = 10,
+    })
+end
+
+return setup