Document the 'experimental.config.utils.schema' module

[andreyaksenov]

Fixes #4279.

New samples

The following new samples were added to demonstrate the main use cases of this module.

Config hierarchy

• config_schema_nodes_scalar
• config_schema_nodes_record
• config_schema_nodes_record_hierarchy (based on config_schema_node_record)
• config_schema_nodes_array (based on config_schema_node_record)
• config_schema_nodes_map (based on config_schema_node_record)

Annotations

• config_schema_annotations (based on config_schema_node_record)

Helper methods

• config_schema_methods (based on config_schema_node_record)

Environment variables

• config_schema_fromenv (based on config_schema_node_record)

Computed annotations

• config_schema_computed_annotations (based on config_schema_nodes_record_hierarchy)

Updated samples

The application_role_http_api sample has been updated to use the new module.

Docs

• https://docs.d.tarantool.io/en/doc/config_utils_schema/reference/reference_lua/config/utils_schema
• https://docs.d.tarantool.io/en/doc/config_utils_schema/platform/app/app_roles/#validating-a-role-configuration (mention a new module)
• https://docs.d.tarantool.io/en/doc/config_utils_schema/reference/configuration/configuration_reference/#configuration-reference-app-cfg (mention a new module)