Allow to ignore specific field in patchers

[Krever]

Right now it is possible to ignore all the redundant fields in the patcher with ignoreRedundantPatcherFields which is significantly unsafe.

I think it might be a good idea to allow to specify the fields to be ignored explicitly. My current use case below contains 3 different possible uses of such a feature.

case class Foo(id: FooId, a: String)
case class Bar(id: BarId, b: Int)
case class MyPatch(id: FooId, a: Option[String], b: Option[Int])

val (foo, bar p): (Foo, Bar, MyPatch) = ???

foo.using(p).ignoreFields(_.id, _.b).patch
bar.using(p).ignoreFields(_.id, _.a).patch

First, the most obvious one is that I want to ignore redundant fields (a when patching Bar and b when patching Foo). This can be achieved with ignoreRedundantPatcherFields yet with explicit specification I'm safe from the situation when I add a field and its omitted from patching accidentally.

Second is that I ignore id when patching Foo because I already know its the same value. Or at least I assume so and if this assumption is wrong (due to a bug) I may end up with a very weird state once data is patched including this id field.

Third is that Bar also contains a field named id which I not only don't want to patch but also this field is of a completely incompatible type. Currently, I have to fall back to copy as I don't know any workaround for this part.

[MateuszKubuszok]

Depends on #538 which in turns depends on #115.