4.x: Supplier in builder

[tomas-langer]

Description

A blueprint can now define a Supplier<T>. If this type is @Configured and the method has @ConfiguredOption, the supplier will be used directly from Config (if used).
This means the supplier will provide the latest value if changes are enabled in config.

Added appropriate test with a mutable configuration.

Resolves #7323
May require rebase after #7400 is merged

Documentation

This enhancement adds support for a typed Supplier in prototype blueprints (Helidon builder).
The following blueprint:

@Prototype.Blueprint
@Configured
interface SupplierBeanBlueprint {
    @ConfiguredOption
    Supplier<String> stringSupplier();
}

will work with io.helidon.config.Config that has support for changes (using polling, file watcher, or an event based config source) in the following way:

• if the SupplierBean is created with config (such as SupplierBean.create(Config) or SupplierBean.Builder.config(Config) is used), the returning supplier will always provide the latest known value from the configuration key string-supplier

Of course the supplier can also be set explicitly (SupplierBean.Builder.stringSupplier(() -> "someValue)) - in this case, the supplier that is provided by user will be used

[trentjeff]

link to something here to support "if changes are enabled".

[tomas-langer]

There is a clear statement "the semantics depend on implementation" - I cannot link to a type that is an implementation of this interface.