Additional docs for ambient/ ztunnel user guides updated for 1.21.0

[srampal]

… functions esp inpod traffic redirection

Description

AMbient/ ZTunnel guide docs update for 1.21.0 functionality and datapath details including inpod traffic redirection.

Reviewers

• [x] Ambient
• [x] Docs
• [ ] Installation
• [x] Networking
• [ ] Performance and Scalability
• [ ] Extensions and Telemetry
• [ ] Security
• [ ] Test and Release
• [ ] User Experience
• [ ] Developer Infrastructure
• [ ] Localization/Translation

[istio-testing]

Skipping CI for Draft Pull Request. If you want CI signal for your change, please convert it to an actual PR. You can still manually trigger a test run with /test all

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[srampal]

@bleggett @dhawton @linsun @yuval-k PTAL

[srampal]

@craigbox @linsun @srampal @dhawton

Did a pass, applied edits to fix outstanding comments.

I'm good if you all are.

I'm good too. @dhawton please go ahead and merge if you are a docs maintainer.

[bleggett]

TY @srampal !