Create endpoint to assign EVM address for ramps

[prayagd]

Context

In order to fix issues regarding Ephemeral key management and storage, this ticket is to create a endpoint where SDK users can assign a fixed EVM address for their ramps.

Todo

• Allow using custom/designated accounts for API clients
• This endpoint can only be used once per 24 hours
• Vortex checks to not fund gas money more than every 24 hours
• Endpoint should allow a value of valid EVM address