[EPIC] Revamp Quick Start Guide and Improve Docs Structure

[eeshaanSA]

Description

The Quick Start guide is the first impression for new users, but it can be more efficient, clear, and engaging. We also see opportunities to improve the overall structure of the docs so users can better navigate and understand PipeCD’s complexity.

Goals

• Make Quick Start easier and faster to follow.
• Cover core concepts
• Improve navigation and organization across docs.
• Ensure technical depth for advanced users while keeping the quick start "quick"

Discussion Prompt

• How can we simplify Quick Start without losing depth?
• What structural improvements would help you (or others) find information faster?
• How can we make sure that the quick start is more 'new contributor' friendly?

Drop your comments below!

[eeshaanSA]

@khanhtc1202 @t-kikuc can you guys help me label these issues appropriately and also maybe make these two issues, this and #6124 type:EPIC? We can then link multiple small Issues/PRs to these issues and make these discussions threads.