Update "Administrative Set" heading to h2 on Add New Work - Relationships pages

[christhepianist]

Descriptive summary

Hyku version 6.0 + commits through cf5a4fc

Rationale

On the Add New Work - Relationships page for all types of works, there are basically 2 sections: choosing an admin set and adding works to a collection. Right now, the eye goes to the "Collections" area because "Administrative Set" uses a smaller font. Since it is just as important (possibly more important as works require an admin set, but not a collection), these should both be headings and at the same level.

Currently "Collections" uses a h2; "Administrative Set" should be the same.
<h2 class="h3 mt-4">Collections</h2>

<div role="tabpanel" class="tab-pane " id="relationships">
--
  | <div class="form-tab-content">
  |  
  | <div class="form-group select optional generic_work_admin_set_id"><label class="control-label select optional" for="generic_work_admin_set_id">Administrative Set

Expected behavior

The 2 headings should use the same heading level.

Actual behavior

One heading is a div; the others is a h2. Both should be a heading, most likely both should be h2.

Steps to reproduce the behavior

1. Open Works
2. Add New Work
3. Choose a work type
4. Create work
5. Relationships