Add DSpace handle to thesis model

[hakbailey]

Why these changes are being introduced:

When theses are published to DSpace, the SWORD submission will return a handle that we want to store in this system.

How this addresses that need:

• Adds dspace_handle field to the thesis model with corresponding test
• Adds dspace_handle field to admin view of thesis info (note, does not add this field to the edit form, as it is not intended to be edited other than by the SWORD submission job)

Relevant ticket(s):

• https://mitlibraries.atlassian.net/browse/ETD-296

Developer

• All new ENV is documented in README
• All new ENV has been added to Heroku Pipeline, Staging and Prod
• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• There are appropriate tests covering any new functionality
• The documentation has been updated or is unnecessary
• The changes have been verified
• New dependencies are appropriate or there were no changes

Requires database migrations?

YES

Includes new or updated dependencies?

NO

[coveralls]

Coverage remained the same at 94.574% when pulling e637cda on etd-296-add-dspace-handle-to-thesis into be47933 on main.