refactor: use TOML for configuration file (#1228)

* refactor: remove jsconfig.json

* chore: remove devcontainer config

* refactor: migrate Hugo configuration from `hugo.yaml` to dedicated `module.toml` and `params.toml` files, and update minimum Hugo version.

* refactor: migrate demo site configuration from `hugo.yaml` to `config/_default/*.toml`

* feat: enable local sidebar avatar for demo site and relocate its image to demo assets.

* feat: migrate demo site to Hugo Modules for theme management.

* fix: wrong config folder name

demo/config/_default/menu.toml

@@ -0,0 +1,13 @@
+[[social]]
+    identifier = "github"
+    name       = "GitHub"
+    url        = "https://github.com/CaiJimmy/hugo-theme-stack"
+    [social.params]
+        icon = "brand-github"
+
+[[social]]
+    identifier = "twitter"
+    name       = "Twitter"
+    url        = "https://twitter.com"
+    [social.params]
+        icon = "brand-twitter"