docs: Update anthropic promptCaching syntax

[bdougie]

Description

[ What changed? Feel free to be brief. ]

Following up on #6145

1. removing the old models listed
2. promptCache syntax added

Checklist

• [x] I've read the contributing guide
• [x] The relevant docs, if any, have been updated or created
• [x] The relevant tests, if any, have been updated or created

Screenshots

[ For visual changes, include screenshots. Screen recordings are particularly helpful, and appreciated! ]

Tests

[ What tests were added or updated to ensure the changes work as expected? ]