Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

ui/static/js/request_builder.js

@@ -1,48 +0,0 @@
-class RequestBuilder {
-    constructor(url) {
-        this.callback = null;
-        this.url = url;
-        this.options = {
-            method: "POST",
-            cache: "no-cache",
-            credentials: "include",
-            body: null,
-            headers: new Headers({
-                "Content-Type": "application/json",
-                "X-Csrf-Token": this.getCsrfToken()
-            })
-        };
-    }
-
-    withHttpMethod(method) {
-        this.options.method = method;
-        return this;
-    }
-
-    withBody(body) {
-        this.options.body = JSON.stringify(body);
-        return this;
-    }
-
-    withCallback(callback) {
-        this.callback = callback;
-        return this;
-    }
-
-    getCsrfToken() {
-        let element = document.querySelector("body[data-csrf-token]");
-        if (element !== null) {
-            return element.dataset.csrfToken;
-        }
-
-        return "";
-    }
-
-    execute() {
-        fetch(new Request(this.url, this.options)).then((response) => {
-            if (this.callback) {
-                this.callback(response);
-            }
-        });
-    }
-}