feat: + SoulSwap DEX on AVAX and FTM

[BunsDev]

Description

Please add the SoulSwap DEX, so we may integrate the 0x API into our upcoming iOS mobile app in September. We are eager to work together and integrate 0x. We have been active for almost 2 years and operate primarily on Fantom Opera and Avalanche Network.

Testing & Simbot Run

Checklist

• [x] Update 0x API documentation (gitbook) if needed (e.g. public facing API change).
• [x] Add tests to cover changes as needed.
• [x] All dependent changes (e.g. RFQ server, Gas Price Oracle) have been deployed (if any).

[BunsDev]

Please let me know if you have any questions or concerns and I will gladly provide any information required to execute this integration. Thanks so much!