DOC Update documentation for GraphQL v4

[maxime-rainville]

This updates some of the existing GraphQL documentation to match up with the new functionality, be a bit clearer, and some formatting/grammar updates.

The new section in the 4.11.0 changelog is mostly copied from the beta/RC changelog but includes a new "What do I need to know to get started?" section linking to relevant additional information (namely how to upgrade custom schemas, and how to build schemas).

Related PR

• MNT Show graphql v4 classes in api.silverstripe.org api.silverstripe.org#99

Parent issue

• https://github.com/silverstripeltd/product-issues/issues/519

[GuySartorelli]

I think you may have committed the wrong file ;p

[GuySartorelli]

I mentioned this on slack as well but in case you haven't seen that:
I think it would make sense to split this up.
Everything that talks about write permissions and which options are available for building the schema should probably go in the general graphql docs section somewhere (if it's not there already) - we can then just link to that. It will be relevant for anyone picking up silverstripe from scratch who wants to know how they should be building their graphql schema into the forseeable future, not just people upgrading from 3.

I think this doc should be explicitly about the fact that there is now a stable v4, what the implications for that are, and some quick info (and links to more detailed info) about upgrading from v3.

Also it'll be worth looking at https://docs.silverstripe.org/en/4/developer_guides/graphql/upgrading/ which I found when I was thinking about this - whether that should just be absorbed into these docs and that file removed, or just linked to from this doc, etc.... but we should avoid duplication as much as we can.

[GuySartorelli]

There is an inconsistency in performance in the docs that I'm not sure how to handle, having done no benchmarking myself.

In the original documentation written by UncleCheese (in 03_building_the_schema.md):

A large schema with 50 DataObject classes exposing all their operations can take up to 20 seconds to generate.

In the new docs written by @maxime-rainville which I've added to 05_deploying_the_schema.md:

While benchmarking schema generation performance, we measured that a schema exposing 180 DataObjects with 1600 relations could be built on-demand in less than 6 seconds on a small AWS instance.

This is a massive discrepancy... which is accurate? Are they both somehow accurate? Is it okay to leave the docs saying what seem to be two conflicting statements, and if not, how should this be handled?

Lots has changed

[emteknetnz]

Thanks for quick turn around

Only thing I'm concerned with here is the ordering of the schema generation options.