✨(theme) add themes management

This is made in order to be able to handle natively multiple themes
for the future light/dark themes and also allow consumers to create
their own.

packages/react/src/components/Button/index.spec.tsx

@@ -68,6 +68,8 @@ describe("<Button/>", () => {
   it("uses custom token", async () => {
     await buildTheme();
     const tokens = await loadTokens();
-    expect(tokens.components.button["border-radius"]).toBeDefined();
+    expect(
+      tokens.themes.default.components.button["border-radius"],
+    ).toBeDefined();
   });
 });