feat: Add CREAM as a liquidity source

[alexkroeger]

Description

Add CREAM to asset-swapper.

CREAM (Crypto Rules Everything Around Me) is a Balancer clone.

Testing instructions

Types of changes

Checklist:

• [x] Prefix PR title with [WIP] if necessary.
• [x] Add tests to cover changes as needed.
• [ ] Update documentation as needed.
• [x] Add new entries to the relevant CHANGELOG.jsons.