Disc 5634 pluggable document store

[owenallenaz]

This was discussed in #5634 . I wasn't sure if you wanted me to revoke the experimental_approximateDocumentStoreMiB or, since that would become a breaking change, if you wanted to keep it out of this PR. I kept it, so that it functions exactly as it did prior. If we are going to keep it, we should probably add a test to the documentStore test file to verify it's actually passing in correctly.

Couple key things I want to call out:

• Added a document entry, it's a little verbose, but this feature doesn't seem to warrant it's own page, and it really should be rarely used, so it seems good enough.
• I added a DocumentStore to types.ts this way we aren't re-specifying the contents of documentStore across many different files. It's definition is using KeyValueCache as suggested.
• The feature supports true, false, undefined or custom object. The downstream code already handled an undefined store luckily so I didn't have to change that at all.
• I am normalizing the value of documentStore so that downstream code always receives a DocumentStore rather than the DocumentStore | boolean complexity that the external constructor accepts.
• To test it I needed to a extension of the main ApolloServerBase so that I could externally call the protected graphQLServerOptions. There might be a better way to accomplish this...

Let me know what you'd like to tweak.

[glasser]

I started by squashing your commits into a single commit and rebasing on main (which involved making a few tweaks based on changes already on main).

Before merging I'm going to do the following:

• add CHANGELOG entry
• minor copy-edits to docs
• Remove experimental_approximateDocumentStoreMiB and document replacement in CHANGELOG (what's the point of marking things as experimental if you can't take them away when there are replacements?)
• Remove ability to set store as boolean. I think null is more appropriate here.

[glasser]

OK, feeling good about this. I probably won't do the actual merge and release until Monday; if you object to any of the changes I've made please let me know @owenallenaz!

There's some formatting issues with the code snippet I added in the API reference doc page. @trevorblades @StephenBarlow thoughts?

[glasser]

It scrolls sideways but at least only this scrolls sideways.

[StephenBarlow]

haha yes, in a world where this codeblock is helpful, this is the preferable solution for its rendering

[glasser]

Unfortunately, if this feature was used in Apollo Gateway (ie, any new ApolloServer call receiving both non-null/undefined documentStore and gateway options), it could lead to a bug where invalid operations could be executed after a schema update. If you are using this feature in a Gateway, we highly recommend upgrading to v3.6.6 which fixes the issue.

The fix is that we now always prefix keys in the document store with a random string that is refreshed each time a new schema is received. We apply this fix in the non-Gateway case too. The fix to the issue also means that the caveat in the docs about not sharing a documentSource across ApolloServer objects has been removed, as this random prefix helps with that case as well.