Add relation between switchers and active configuration

My proposal is about connecting environment_indicator.indicator and withenvironment_indicator.switcher.*

If we have this connection, we have next options:
1. Automatically detect current env based on current domain/path
2. Create service to get active env.
3. (My use case) Create condition plugin that can be used to show/hide blocks in specific environments.

Simplest way is to add id key to environment_indicator.indicator.

I wrote working patch, it don't do anything if id is not present in environment_indicator.indicator config.
If configured properly, then you can setup any block to show/hide based on current environment.

I need help in testing & writing docs.
Also admin/config/development/environment-indicator/current should be updated to provide UI way.

Another way to make progress on module's architecture is to how environment_indicator_page_top is work, provide drupal 8 services, etc.