Change create_transaction for further input validation

[ntua-el19096]

For the time being /create_transaction endpoint allows API callers to make the app crash based on their input. We should be more strict to input validation. Also introduce a check that does not allow the caller to send make a transaction with the sender and recipient address being the same.

[ntua-el19848]

Other than

a check that does not allow the caller to send make a transaction with the sender and recipient address being the same

what other case leads to crash?

[ntua-el19848]

THOUGHTS:

• only fees should be allowed from sender to same receiver

[ntua-el19848]

Now it works for same receiver_id, sender_id only in fees

In COINS-MESSAGES

In FEES

DONE IN COMMIT

SHA eadb9e5da5bc3bcb18d4b47afc9c956bc552696a