Create transaction validation endpoint for SPUR wallet transfers

[AmirAgassi]

Description

Create an endpoint to validate blockchain transactions sent to the SPUR wallet and automatically update investment intention status.

Checklist

Before submitting this ticket, make sure this ticket:

• Is labelled properly.
• Has the SPUR project assigned to it.
• Has an assigned milestone.

And lastly:

• Once someone picks up this ticket, make sure to assign it to a developer.