Implement on_shutdown API

Implemented on_shutdown API, which allows to register functions
that will be called when the tarantool stopped. Functions will
be called in the reverse order they are registered. So the module
developer registers one fuction that starts module termination and
waits for its competition. This function should be fast or used an
asynchronous waiting mechanism (coio_wait or cord_cojoin for example).

Closes #5723

@TarantoolBot document
Title: Implement on_shutdown API
Implemented on_shutdown API, which allows to register functions
that will be called when the tarantool stopped. Functions will
be called in the reverse order they are registered. So the module
developer registers one fuction that starts module termination and
waits for its competition. This function should be fast or used an
asynchronous waiting mechanism (coio_wait or cord_cojoin for example).