v0.7.0 release notes

In this release, we added the below items:

• A new endpoint GET /card-integrators/float to get float balance for a card integrator
• Reduced the allowed transaction types for POST /cards/{id}/mock-transaction to deduct and deduct-reversal only.
• Improvements to our error handling mechanisms
• Broadcast 2 more events from our system card.reverse-transaction and user.kyc-verification
• Added a checksum attribute on the webhook payload to allow integrators to confirm that the webhook event is coming from us