fix: add headers to cache key

[alexandernanberg]

Fixes #4486
Fixes #5608

Requests with different headers should not be memoized or use the same cache key. This PR add all the headers to the cache key

[apollo-cla]

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[glasser]

(First note: apollo-datasource-rest is not being very actively maintained at the moment. You may want to investigate alternatives such as the newer apollo-datasource-http.)

This change seems to be unnecessarily aggressive. Using all headers in the cache key is likely to result in few cache hits.

#4486 can be fixed by overriding cacheKeyFor yourself, as the comments above it suggest. So I think the following could be solutions:

• Better documentation encouraging you to override cacheKeyFor
• Making it easier to take headers into account by providing a place to pass a list of relevant headers instead of requiring you to override cacheKeyFor
• Maybe including a few specific headers by default (such as authorization and cookie) like we do in Studio usage reporting

That said #4486 is also based on a misunderstanding of the data source lifecycle, and I've closed it.