Topper API support

[donnyquixotic]

Description Add endpoint to generate bootstrap token used for Topper Pay widget link forwarding

Tasks

• [x] add widget pk as AWS secret
• [x] add lib to generate token
• [x] add route that accepts address as optional query param
• [x] add optional sandbox flag for testing
• [x] exclude route from swagger

[pmjanus]

Blocks wallet topper integration.