tiproxy: add tiproxy topology definition to the usage section

[djshow832]

What is changed, added or deleted? (Required)

close #20084

Add tiproxy topology definition to the usage section

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-24 04:53:02.628581791 +0000 UTC m=+415709.959501188: ☑️ agreed by dveeden.
• 2025-01-24 08:53:39.149879585 +0000 UTC m=+430146.480798987: ☑️ agreed by hfxsd.

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