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/markup.toml

@@ -0,0 +1,24 @@
+[goldmark]
+    [goldmark.extensions]
+        [goldmark.extensions.passthrough]
+            enable = true
+            [goldmark.extensions.passthrough.delimiters]
+                block  = [["\\[", "\\]"], ["$$", "$$"]]
+                inline = [["\\(", "\\)"]]
+    [goldmark.renderer]
+        ## Set to true if you have HTML content inside Markdown
+        unsafe = true
+
+[tableOfContents]
+    endLevel   = 4
+    ordered    = true
+    startLevel = 2
+
+[highlight]
+    noClasses          = false
+    codeFences         = true
+    guessSyntax        = true
+    lineNoStart        = 1
+    lineNos            = true
+    lineNumbersInTable = true
+    tabWidth           = 4