Update upgrading Neutrino guide for v7->v8

[eliperelman]

As always, a new major release will bring breaking changes. We will need to update the upgrading Neutrino guide for v8, outlining the breaking changes, but also listing features.

[edmorley]

I'm still catching up on all the older recent review requests and PRs, but thought I'd comment on this new one first. I was thinking that perhaps we should turn the migration guide into a page that covers all versions? When updating several versions at once it's currently a bit of a pain to have to trawl through the old docs to find the necessary interim migration steps.

[eliperelman]

I agree, let's do it!

[helfi92]

I don't mind doing this :)

[eliperelman]

@helfi92 go for it 😃

[helfi92]

What are the migration points to mention for v7 -> v8.

[eliperelman]

I'd have a look through the landed PRs, and specifically the ones tagged breaking changes.

[eliperelman]

@helfi92 I think we are close to shipping, so we can move forward with this now.

[helfi92]

I'm on it 💪