Temporary: move static files into content

During migration, while we launch Redocly with -d content, the static
files need to be in content. Eventually, when we stop using -d, we need
to move the files again.

Previously:
/assets : static assets used by templates
/img : images used in documentation (mostly)

Now:
/content/static : static assets used by templates
/img : images used in documentation (mostly)

Eventually:
/static : static assets used by templates
/docs/img : images used in documentation

content/static/js/code-samples.js

@@ -0,0 +1,18 @@
+$(document).ready(() => {
+  $(".single_lang input").change((event) => {
+    const lang = $(event.target).val()
+    const lang_checked = $(event.target).prop("checked")
+
+    if (lang_checked) {
+      // Enabling a language
+      //$("#input_all").prop("checked", false)
+      $("#code_samples_list .card").hide()
+      $(`#code_samples_list .card.lang_${lang}`).show()
+    }
+    // Disabling a language? Let the other element's handler do it
+  })
+  $("#input_all").change((event) => {
+    const lang = $(event.target).val()
+    $("#code_samples_list .card").show()
+  })
+})