Permit detailed error message in `EntityCommandHandler`

# Feature Request

At the moment the abstract method `EntityCommandHandler.modify` just returns a boolean, that means that, in case of error, there's no chance for the implementation to return a message in the returned `CommandResult` to the caller.

The proposal would be to change the signature of the `modify` method to return a `CommandResult`.
This could be put in place using deprecations, to permit a smoother transition.

## Which Areas Would Be Affected?

_e.g., DPF, CI, build, transfer, etc._

## Why Is the Feature Desired?

_Are there any requirements?_

## Who will sponsor this feature?

_Please @-mention the committer that will sponsor your feature_.

## Solution Proposal

_If possible, provide a (brief!) solution proposal._