config: use vshard-ee if available

The new closed-source `vshard-ee` module was recently introduced. It is
based on the open-source `vshard` module and, as far as I know, provides
the same API.

Let's configure `vshard-ee` in the same way as `vshard` if sharding is
enabled in tarantool's configuration.

Prefer `vshard-ee` if both are available.

Fixes https://github.com/tarantool/tarantool-ee/issues/815

@TarantoolBot document
Title: config: vshard-ee is now supported

The declarative configuration supports `vshard-ee` in addition to
`vshard` since Tarantool 3.1.1 and 3.2+.

`vshard` is mentioned in the documentation at least [here][1]. All such
places should be updated to mention both `vshard-ee` and `vshard`.

[1]: https://www.tarantool.io/en/doc/latest/reference/configuration/configuration_reference/#sharding