Add validator for forms and validation annotations to model objects

[Eimh]

It might be useful to add validators so that we can organize and deliver feedback when constructing invalid objects.

We will need to add the following dependency:

<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>7.0.0.Final</version>
</dependency>