[NU-1772] Fix line breaks in ScenarioActivities db table

[mgoworko]

Describe your changes

Plaintext activity details from old tables (for example for migration or automatic update) were migrated as part of the JSON in the new table. Newlines were incorrectly migrated as line breaks instead of \n in previous migrations.

Checklist before merge

• Related issue ID is placed at the beginning of PR title in [brackets] (can be GH issue or Nu Jira issue)
• Code is cleaned from temporary changes and commented out lines
• Parts of the code that are not easy to understand are documented in the code
• Changes are covered by automated tests
• Showcase in dev-application.conf added to demonstrate the feature
• Documentation added or updated
• Added entry in Changelog.md describing the change from the perspective of a public distribution user
• Added MigrationGuide.md entry in the appropriate subcategory if introducing a breaking change
• Verify that PR will be squashed during merge

[mk-software-pl]

Do we need a changelog for that? Or this is just a fix to some features not released, so there is no need to mention that?