Create indexes in models and migration files

[acwhite211]

Fixes #7482

Create indexes mentioned in the issue into the models and migration files. Some of the indexes mentioned were already present in the existing model, the rest have been added.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone
• Add pr to documentation list
• Add automated tests
• Add a reverse migration if a migration is present in the PR

Testing instructions

• See that the new migration step for adding the indexes completes successfully.
• Use the QB on fields that have been indexed to see that they run correctly and in a timely manner.