Add tabbed instructions for Core & Zero on "Get Started"
Follow-up to #1726

What's incorrect or missing?

• No direct path for users to choose Pomerium Core or Zero instructions

What's the resolution?

• Introduce tabs or toggles on the "Get Started" page for each offering
• Make sure the differences in steps are clearly separated

Follow-up question

• Are the steps for Core vs. Zero significantly different, or mostly similar with a few key changes?