feat: add fragments server side

[Ariel-Dayan]

Allow clients that send queries to use predefined fragments on the server side.
The goal:

1. Shorten the query for every client by avoiding to repeat the fragment declaration.
2. Allow the client to have dynamic fragments that are updated server side. For example, if a field was added to the schema server side, the fragment will update accordingly.

[acao]

to follow conventions elsewhere, we might accomplish this via graphql-config where folks are already using similar capability for IDE tooling? but it should also be possible without graphql-config

[acao]

@Urigo what do you think about graphql-config plus express-graphql? I know we've been mostly focused on this for dev tooling