Refactor tutorial card name and left-side menu to reduce redundancy

[jimmychu0807]

As Sacha pointed out here. Now if we want to update the title of a tutorial. We actually have to updated them in three places:

• DevNavMenu.tsx
• pages/tutorials/v3.tsx
• v3/tutorials//index.mdx

Will be good if the title on the left side menu (currently defined in DevNavMenu.tsx), the tutorial name on the card (defined in pages/tutorials/v3.tsx), are all read and built from the tutorial content page index.mdx. So we only have one source of truth. We will need to introduce a new frontmatter property, order, in mdx content page to determine the order of tutorials being laid out in tutorial index page.