Bean validation config to allow missing values or other settings

[kringol]

Continuation of https://github.com/lightbend/config/pull/602. Taking into account the feedback, etc

The purpose of this change is to provide a mechanism to configure the bean factory internal workings, and in this particular case, to provide a setting to allow missing field values and keep whatever value was originally assigned to the bean or null, instead of throwing an a validation error. By default such config is disabled, to keep the current behavior as it is and provide a configuration mechanism similar to other sections of the library

[romank8k]

Are there plans to merge this pull request? I'm also in need for a solution to #440

[kringol]

Waiting for @havocp and the team to review/approve prepare the next release i guess. Not sure about the timelines.

[avillev]

@havocp @andreaTP @johanandren @2m

Sorry to tag that many mergers but, what should we do to get feedback or merge that PR? It has been a while and I kind of need that improvement too for my project 👍

[tadhgpearson]

This functionality would be really useful (for me anyway!) but this PR's been open for a long time. What is the barrier to merging this?

[ennru]

We do not intend to extend the functionality of "Typesafe Config" further. See https://github.com/lightbend/config#maintained-by