Pico Config Improvements

[trentjeff]

Config improvements:
Currently we need to set the config through bootstrap. I think we should a concept of two configs:

• a bootstrap config (by default only uses system properties and env vars) to prepare pico
• a config that is constructed as a Service in Pico (and can use other services, such as ConfigSource, Mapper etc.) to create the configuration tree for runtime

[tomas-langer]

We currently support creating Config as a service in registry.
It now only supports custom ConfigSource

[tomas-langer]

The new configuration approach for helidon-service-inject supports both configuration created by user and registered through GlobalConfig and a configuration created within the service registry.
The "bootstrap" configuration will use either the global config (if present), or a new configuration instance created through Config.create().
The "in-registry" config instance gathers services for the registry itself (such as parsers, filters, sources etc.).