Update customer-facing GraphQL docs with new GraphQL deprecation process
This issue is part of the Epic &7155 (closed). Please see that Epic for more context.
About
We should update our customer-facing GraphQL docs with the information that breaking changes will only happen on major releases and that deprecations will be announced in a release post at least 2 milestones prior. This brings it into line with https://about.gitlab.com/handbook/product/gitlab-the-product/#process-for-deprecating-and-removing-a-feature. We should also add a link to https://docs.gitlab.com/ee/update/deprecations.
Edited by Luke Duncalfe