Add more attributes to the blob GraphQL API

What does this MR do?

ide_edit_path and can_modify_blob both have implementations in BlobHelper, which are difficult to extract out. For now, just include the required helpers to get access to the code.

In the future, we should be able to delete the existing FE for viewing the repository, and at that point we should also be able to move this code from BlobHelper and into BlobPresenter more easily.

external_storage_url has its implementation in ApplicationHelper. Long term, moving this seems less likely. It probably fits better in a URL generation location like GitlabRoutingHelpers, but let's not try to tackle that as part of this MR.

Changelog: added

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #323195 (closed)