Add support for custom headers and migrate from legacy auth

- Introduced CustomHeaders component for managing custom headers.
- Updated Sidebar to include CustomHeaders component.
- Enhanced useConnection hook to handle custom headers and legacy auth migration.
- Added tests for custom headers functionality.
- Updated package.json and package-lock.json for new dependencies.

client/src/components/__tests__/Sidebar.test.tsx

@@ -50,6 +50,10 @@ describe("Sidebar", () => {
     setEnv: jest.fn(),
     bearerToken: "",
     setBearerToken: jest.fn(),
+    headerName: "",
+    setHeaderName: jest.fn(),
+    customHeaders: [],
+    setCustomHeaders: jest.fn(),
     onConnect: jest.fn(),
     onDisconnect: jest.fn(),
     stdErrNotifications: [],