Refactor large spec (spec/requests/datacite_dois_spec.rb)

[jrhoads]

Purpose

Breaks the ~5k spec into smaller focused specs.
Two results

1. Greater granularity when an area needs to change
2. Spread specs out when run in a parallel ci setting.

Related to #1248

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

Reviewer, please remember our guidelines:

• Be humble in the language and feedback you give, ask don't tell.
• Consider using positive language as opposed to neutral when offering feedback. This is to avoid the negative bias that can occur with neutral language appearing negative.
• Offer suggestions on how to improve code e.g. simplification or expanding clarity.
• Ensure you give reasons for the changes you are proposing.