docs: update playground example to use chained if conditions (#1287)

## This PR

- update playground example to use chained if conditions

### Related Issues

Fixes #1263

### Notes

The docs already described this behavior. This PR updates the playground
example.

https://flagd.dev/reference/flag-definitions/#conditions

### How to test

Use the progressive rollout example in the playground.

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Signed-off-by: Michael Beemer <[email protected]>
Co-authored-by: Todd Baert <[email protected]>