[WEB-1657] dev: admin application code structuring. (#4867)

* [WEB-1657] dev: admin application code structuring.

* chore: update mobx-react-lite import to mobx-react.

admin/core/components/auth-header.tsx

@@ -0,0 +1,92 @@
+"use client";
+
+import { FC } from "react";
+import { observer } from "mobx-react";
+import { usePathname } from "next/navigation";
+// mobx
+// ui
+import { Settings } from "lucide-react";
+// icons
+import { Breadcrumbs } from "@plane/ui";
+// components
+import { SidebarHamburgerToggle } from "@/components/admin-sidebar";
+import { BreadcrumbLink } from "@/components/common";
+
+export const InstanceHeader: FC = observer(() => {
+  const pathName = usePathname();
+
+  const getHeaderTitle = (pathName: string) => {
+    switch (pathName) {
+      case "general":
+        return "General";
+      case "ai":
+        return "Artificial Intelligence";
+      case "email":
+        return "Email";
+      case "authentication":
+        return "Authentication";
+      case "image":
+        return "Image";
+      case "google":
+        return "Google";
+      case "github":
+        return "Github";
+      case "gitlab":
+        return "GitLab";
+      default:
+        return pathName.toUpperCase();
+    }
+  };
+
+  // Function to dynamically generate breadcrumb items based on pathname
+  const generateBreadcrumbItems = (pathname: string) => {
+    const pathSegments = pathname.split("/").slice(1); // removing the first empty string.
+    pathSegments.pop();
+
+    let currentUrl = "";
+    const breadcrumbItems = pathSegments.map((segment) => {
+      currentUrl += "/" + segment;
+      return {
+        title: getHeaderTitle(segment),
+        href: currentUrl,
+      };
+    });
+    return breadcrumbItems;
+  };
+
+  const breadcrumbItems = generateBreadcrumbItems(pathName);
+
+  return (
+    <div className="relative z-10 flex h-[3.75rem] w-full flex-shrink-0 flex-row items-center justify-between gap-x-2 gap-y-4 border-b border-custom-sidebar-border-200 bg-custom-sidebar-background-100 p-4">
+      <div className="flex w-full flex-grow items-center gap-2 overflow-ellipsis whitespace-nowrap">
+        <SidebarHamburgerToggle />
+        {breadcrumbItems.length >= 0 && (
+          <div>
+            <Breadcrumbs>
+              <Breadcrumbs.BreadcrumbItem
+                type="text"
+                link={
+                  <BreadcrumbLink
+                    href="/general/"
+                    label="Settings"
+                    icon={<Settings className="h-4 w-4 text-custom-text-300" />}
+                  />
+                }
+              />
+              {breadcrumbItems.map(
+                (item) =>
+                  item.title && (
+                    <Breadcrumbs.BreadcrumbItem
+                      key={item.title}
+                      type="text"
+                      link={<BreadcrumbLink href={item.href} label={item.title} />}
+                    />
+                  )
+              )}
+            </Breadcrumbs>
+          </div>
+        )}
+      </div>
+    </div>
+  );
+});