Port should not be nullable

[vosi]

The protocol field in NetworkNode model should not be null or empty. It should have the default set as 80.

Reason,
IP, protocol, port
1.1.1.1, HTTP, null
1.1.1.1, HTTP, 80
will be 2 different nodes, for the system, while in reality its the same node

Also, there should be a data migration in Validator and Bank projects to replace null or empty fields with default 80

https://github.com/thenewboston-developers/thenewboston-python/blob/development/src/thenewboston/models/network_node.py#L14

[YashovardhanSingh]

@buckyroberts #53
Account Number: 38a99b8f1916eab0471ca1df26e7fe5e71d845e6ea5b233cd3d93a75097ea2d6

[angle943]

@vosi @buckyroberts please DM me when this has been completed & merge