[apollo-datasource-rest] Add option to disable GET cache

[smyrick]

Fixes #6603

By default, RESTDataSource caches all outgoing GET requests in a separate memoized cache from the regular response cache. It makes the assumption that all responses from HTTP GET calls are cacheable by their URL.
If a request is made with the same cache key (URL by default) but with an HTTP method other than GET, the cached request is then cleared.

This change adds a new class property requestCacheEnabled (which defaults to true to match current behavior) which allows users to disable the cache. You might want to do this if your API is not actually cacheable or your data changes over time.

Separately it documents this feature exists and adds more info about how to set a TTL for the entire HTTP cache

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[smyrick]

Part of the issue was also that this feature was undocumented so I have added some basic info about the RESTDatasource properties and methods. I would prefer to review the code first and get iterative changes into the docs as needed.

[smyrick]

cc @Jaxolotl

[smyrick]

cc @trevor-scheer and @glasser.

I can port my changes over to the new package, but this change is still relevant to anyone using ASv3 today or whoever will in the future with respect to the doc changes. Can I get a review for this one?

https://github.com/apollographql/datasource-rest

[trevor-scheer]

Can you please add why someone would want this behavior to the PR description? Totally fine if it's the same blurb that I asked to be added to the docs, just want people to understand why they'd disable it.

We can delete the changeset, and add an entry to CHANGELOG - sorry, we had the bot enabled for v4 development (glasser's since disabled it) which made it confusing for dev on main since we're not using it for v3 things.