Update campaign_contact.updated_at on change

[sjwmoveon]

Fixes #2361

Description

Add a trigger on the campaign_contact table to update the "updated_at" column whenever changes are made to the table.

Checklist:

• I have manually tested my changes on desktop and mobile
  N/A - change is a database migration
• The test suite passes locally with my changes
• If my change is a UI change, I have attached a screenshot to the description section of this pull request
• My change is 300 lines of code or less, or has a documented reason in the description why it’s longer
• I have made any necessary changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
  N/A - change is a database migration
• My PR is labeled [WIP] if it is in progress

[crayolakat]

Looks good!!