Add query meta

[Khatskevich]

For testing and debugging purposes, we need more information about a query execution
I suggest at least add:

1. Used indexes/warnings that indexes were not used
2. Exec time
3. Number of retrived objects
4. Number of returned objects
5. Number of lookups

Until we do not have strict vision of how it should look like, I suggest add this information in any free form (at least text description, or raw data (index structures themselve)).

[Totktonada]

We can collect it in qcontext and then create API for accessor_general <-> tarantool_graphql to pass meta and then return it in tarantool_graphql.

[Totktonada]

Meta was added, but some information still doesn't provided:

1. Used indexes/warnings that indexes were not used
2. Exec time

[Totktonada]

I'm going to archive the repository. I'll proceed as follows:

• Mark all open pull requests with the archived label and close.
• Mark all open issues with archived and wontfix labels and close.
• Archive the repository.

Consider the following projects:

• https://github.com/tarantool/graphql
• https://github.com/tarantool/graphqlapi
• https://github.com/tarantool/graphqlide