Due to changes in the third-party `graphql-upload` package which Apollo
Server utilizes to implement out-of-the-box file upload functionality, we
must drop support for file uploads in versions of the Node.js engine prior
to v8.5.0.  Since file uploads are supported by default in Apollo Server 2.x,
and there is an explicit dependency on `graphql-upload`, we must
prevent users who are affected by this mid-major-release deprecation by
being surprised by the sudden lack of upload support.

By `throw`-ing an error at server startup for affected users, we certainly
are breaking a semantic versioning agreement for these users, however with a
relatively simple ergonomic (setting `uploads: false`) we allow those users
who are NOT utilizing file uploads (as we believe is the case with a
majority) to continue using their version of Node.js until it reaches the
end of its supported lifetime (as dictated by its Long Term Support
agreement with the Node.js Foundation).  If we did not `throw` the error at
server start-up, those affected may not notice since they may update and start
their updated server without noticing the impending chance of failure when
someone tries updating!

Apollo Server 2.x has attempted to maintain full compatibility with versions
of Node.js which are still under Long Term Support agreements with the
Node.js Foundation.  While this continues to mostly be true, file uploads
are an exception which we've now had to make.

Third-party open-source projects must absolutely do what's best for their
project.  From an architecture standpoint, I suspect that we (the designers
behind Apollo Server) are mostly to blame for this.  Namely, it's unfortunate
that we had made such an incredibly coupled integration with a third-party
package that we restricted our users from incrementally adopting the
changes (and new/improved functionality) of, in this particular case,
the `graphql-upload` package.  I hope we can take better care with decisions
like this in the future!

Lastly, this commit also adds documentation to help those affected.

Now that there are specific versions of Node.js which don't support file
uploads (namely, <= 8.5.0) we need to explicitly disable uploads on those
versions, similar to how those users must opt-in to that behavior by setting
`uploads: false` in their Apollo Server constructor options.

This effectively accomplishes exactly that, but only when necessary.

I hope to actually remove this limitation, but I'm going to iterate on it
first.  This also just switches to a `NODE_MAJOR_VERSION` constant from the
`apollo-server-integration-testsuite` rather than using the GTE function on
the same input since...math.

This commit looks way more complicated than it really is thanks to Prettier
trying to be helpful.

All I've done is add `NODE_MAJOR_VERSION === 6` as a version NOT to test
uploads for, in an effort to fix the failing tests (failing appropriately
since Node.js 6 with file uploads throws an error right now and cannot run
uploads anymore.).

This commit again looks quite complicated, but's merely an over-complication
inflicted by Prettification.  Disabling whitespace differences when viewing
this commit, the functional change here is that we no longer skip many file
upload tests when the (semver) major segment of `process.version` is `10`.

I couldn't be happier to get rid of this exception for file upload tests on
Node.js 10, which was an unfortunate reality of the non-updated
`graphql-upload` module world we previously lived in.

Thanks, @jaydenseric, for the newfound (to us!) Node.js upload support!

…ode-8.5