Support "vshard_router" CRUD operation option

[akudiyar]

This option is necessary if a space is not shared and is present on a router node only, or a non-standard group name is used for it.

Documentation: See the option description, for example, in https://github.com/tarantool/crud#insert

Discussion:

• the name of this option is quite confusing. Also, I don't understand why we have a union typed option instead of two mutually exclusive options with descriptive names here. I'd rather rename it in the driver, and create an issue in tarantool/crud for fixing it there.