Add db.provider to replace db.adapter

[timleslie]

Now that we only support Prisma the question isn't "which keystone adapter do you want?" as much as "which Prisma provider do you want to use?". This deprecates db.adapter, which will be removed in the next release.

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🦋 Changeset detected

Latest commit: 64ed79d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@keystone-next/website	Minor
@keystone-next/keystone	Minor
@keystone-next/types	Minor
@keystone-next/test-utils-legacy	Patch
@keystone-next/auth	Major
@keystone-next/example-auth	Patch
@keystone-next/app-basic	Patch
@keystone-next/example-ecommerce	Patch
keystone-next-app	Patch
@keystone-next/example-roles	Patch
@keystone-next/example-sandbox	Patch
@keystone-next/example-todo	Patch

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[timleslie]

@mitchellhamilton Is there a better way of saying "one or the other, but not both"?

[emmatown]

Not really

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[emmatown]

Just want to explicitly block this on my review while I check things because I think I will have comments

[emmatown]

Looks fine except for the @deprecated bit: can you remove the colon(it doesn't make sense and looks weird when shown in editors) and add the @deprecated comment to both the adapter?: undefined cases so that the adapter option shows as deprecated in autocomplete (currently in this PR, it doesn't look like this)?