[Config] Rework the main 'Configuration' topic

Related doc issue(s): https://github.com/tarantool/doc/issues/4190

Product: Tarantool
Since: 3.0/3.1
Root document: https://www.tarantool.io/en/doc/latest/concepts/configuration/
SME: @ Totktonada

Details

Below are some things that can be improved:

• Remove the Configuration options overview section after fixing https://github.com/tarantool/doc/issues/4012.
• Update the structure of the Configuration section:
  • Cluster configuration
    • Centralized configuration storages
    • Configuration in code (legacy)
• Emphasize the difference between two configuration approaches: in a file and config storage. For example, the diagrams from this topic can be moved to the main topic.
• Describe some examples of maintaining consistency in a file config: network folder, external tools for delivering the config file to different machines.
• Consider adding diagrams that help a reader understand main concepts, for example:
  • Config and one instance
  • Config and several instances on one machine
  • Config and several instances on different machines
  • Other ideas: https://github.com/tarantool/doc/issues/3849#issuecomment-1809456024
• Add information about the config module API: https://github.com/tarantool/doc/issues/3662.
• Take Roles into account: https://github.com/tarantool/doc/issues/3702.

Possible topic structure

• Configuration sources
  • Local
  • Сentralized
    Env vars.
• Configuring a cluster topology
  • Instance
  • Replica set
  • Group
  • Global
  • Scopes (merging)
• Developing applications
  • app/app_cfg
  • roles/roles_cfg
• Configuration values
  • Value type (string, number, array, dynamic (sync quorum), ...)
  • Default values
  • Predefined variables
• Environment variables
• Loading config from external storage (config.context)
• Configuration precedence
• Reloading configuration

Start with the root Configuration topic and review the related configuration_etcd topic plus issues 4190, 4012, 3662, 3702, and 3849. Map the proposed structure and decide how the configuration approaches, cluster concepts, examples, diagrams, API, Roles, and reloading material fit together. Done means the main topic is reorganized and the listed gaps are addressed or linked clearly.