chore(apollo): Fix publishing errors with apollo-appsync

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:
The signing key was only being set for Android projects, resulting in no signature generating for apollo-appsync. You need signature files to publish the artifacts to maven central. Therefore I moved the setting of the required extras outside the check for the Android plugin.

How did you test these changes?
(Please add a line here how the changes were tested)

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.