Unified configuration management framework

[Lloyd-Pottiger]

Feature Request

Is your feature request related to a problem? Please describe:

Now, the configuration is a mess. Some are configured by toml file, and some are recorded in the dbms/src/Interpreters/Settings.h. We initialize components by global_context and the default value has been decided in compiler time, even if the configuration has not been loaded, components can run smoothly.
There are cause some potential risks:

1. Some components initialize with default settings rather than the configuration in the input configuration file.
2. The configuration has changed during running, but we can not perceive it.

Describe the feature you'd like:

We need a unified configuration management framework in order to

1. manage the configuration of different components together
2. real-time awareness of the configuration.
3. an interface to get the configuration for users

Milestone

• collect and classify all the configuration
• add a controller to manage configuration globally
• use the controller in all tiflash components