Config with injection

[tomas-langer]

Resolves #7079

Config documentation notes

Helidon config API (helidon-common-config)

There is a new class:
io.helidon.common.config.GlobalConfig

This class can be used to set global configuration to be used by Helidon components. The configuration must be set as the first thing, before Helidon components
are invoked, or Helidon main class is called.
If no configuration is set, the usual Config.create() is used to obtain configuration either from default sources, or using meta configuration.

Helidon config
ConfigSource interface is now marked as a @Contract for Helidon Injection
ConfigProducer is a new @Singleton service that combines the discovered ConfigSource from Helidon Injection, with the discovered configuration (from GlobalConfig) and creates a new config (unless an explicit config instance is set using GlobalConfig - in such a case it is used AS IS).
This means that when io.helidon.common.Config is injected into any service using Helidon Injection, this combined config instance will be provided.

PR notes

helidon-config dependency had to be removed from all pico modules, so we can generate service code in config module. The tests were moved to appropriate location in pico/tests, currently using the same packages, to allow calling package local methods.

Wow this caused quite a mayhem in our dependency management for jakarta.inject-api. Investigating

Follow up issue: #7081

[ljamen]

Reviewed java files. No docs currently associated with this draft PR. Documentation will be captured in a separate PR.

[tomas-langer]

Reviewed java files. No docs currently associated with this draft PR. Documentation will be captured in a separate PR.

I have added you because of the comments in the PR description - those are relevant for Config documentation once we merge this.
Thanks

[tomas-langer]

Rebased on main and fixed APT dependencies.