Rebase fork changes on top of upstream

[ValentinH]

In this PR, we rebase the fork on top of the latest upstream master branch.
Some changes that were made before are not needed anymore because similar features were added on upstream:

• "fix: create a custom scalars map with some Hasura specific types" (1cb5233) => we can use the new Scalars feature

We still have to maintain 2 differences for now:

• fix: use null instead of undefined for non-required fields (f298564) - see issue
• fix: use literal union type instead of enums (7b2c6cb) - see issue

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I've tested this new version on our codebase and I see multiple reasons to not update at the moment:

• everything is slower, fields auto-completion is not instant anymore. I guess it will be even worse on non M1 machines.
• the new Scalars feature which I expected to replace one of our patch, isn't matching all our requirements. Especially, it doesn't properly type the parameters that can be passed to queries/mutations filters. It only typed the returned data.
• the new way to use Apollo hooks is a heavy breaking changes that would have us touching a lot of code in our codebase. Indeed, we would not use useTypedQuery() and useTypedMutation() anymore but would have to first create the query/mutation with the typedGql function and then directly call the original useQuery() or useMutation() hooks

In this state, I'm pausing the upgrade effort for now.