config: expose experimental.config.utils.schema

The module is renamed from `internal.config.utils.schema` to
`experimental.config.utils.schema` without changes.

It is useful for validation of configuration data in roles and
applications.

Also, it provides a couple of methods that aim to simplify usual tasks
around processing of hierarchical configuration data. For example,

* get/set a nested value
* apply defaults from the schema
* filter data based on annotations from the schema
* transform a hierarchical data using a function
* merge two hierarchical values
* parse environment variable according to its type in the schema

See https://github.com/tarantool/doc/issues/4279 for an in-depth
description.

Fixes #10117

NO_DOC=https://github.com/tarantool/doc/issues/4279