Update Parameter validation features

I went through the Read Only Parameters PR https://github.com/ros2/rclcpp/pull/495 and I experimented a little with Parameters validation via set_on_parameters_set_callback.

I think that there are 2 important features missing:

• In some cases READ_ONLY is too restrictive. The following use-cases should be also possible: a parameter can be modified, but it can't be deleted; a parameter can be modified only by the node that declared it.
• Currently it's possible to change the type of a parameter. To me this looks something that should be enabled only in particular cases, while the default behavior is that if a node declares a parameter to be bool I can't set it to a string or something else.

Both these things can be already done with a custom callback in set_on_parameters_set_callback, but it's quite verbose and not well documented.

Do you agree that these features should be present?
In case, should they be part of the ParameterDescriptor? I was reading about creating a custom structure for parameter constraints, but I haven't found a conclusion.

Start by reviewing the ParameterDescriptor API and the set_on_parameters_set_callback mechanism referenced in the issue, along with the linked read-only parameters pull request. Determine whether the proposed deletion, ownership, and type constraints have an agreed design. Done means an accepted API direction with documented behavior and corresponding implementation scope.