Improve validation mechanism and review validation in resolvers

[dlpzx]

Is your idea related to a problem? Please describe.
There are 2 parts of the code that could be enhanced:

1. resolvers is where we validate the api input and call the services, but in some cases this validation happens solely in the service
2. validation in the services involves a lot of lines of code, there must be a better way to build RequestValidators

Describe the solution you'd like

1. api input validation in resolvers
2. simple validation where it is needed in services --> at the end services can be used by other services, so we need to ensure that the input is valid

P.S. Don't attach files. Please, prefer add code snippets directly in the message body.