improve zio config support for Map where key is a String WrappedType

[loathwine]

Summary

Adds DeriveConfig instances for Map[B, V] where B is a newtype or subtype wrapping String.

Problem

Previously, if you had a newtype key for a Map in your config, derivation would fail:

type UserId = UserId.Type
object UserId extends Newtype[String]

case class Permissions(userAccess: Map[UserId, String])

// This would fail to derive:
// deriveConfig[Permissions]

Even though DeriveConfig[Map[String, V]] exists, there was no way to derive DeriveConfig[Map[UserId, V]].

Solution

Two new given instances in ZioConfigInstances:

• validatedMap — for validated newtypes/subtypes, applies validation to each map key
• simpleMap — for simple (unvalidated) newtypes/subtypes, wraps each map key directly

These also compose for stacked types like Newtype[ValidatedSubtype].

[loathwine]

Related zio-config#1381
I wonder if the fix should be in zio-config instead. I'll take a look if it is easy to add there.

[loathwine]

Created PR zio-config#1658. It is arguably a better fix. Then neotype would just need to derive ConfigKeyDecoder in the usual straight forward way. Not sure if/when it will be approved and released though.

Should I close this PR or leave it open?