Code Review Bench PR #31198 - EXP-5874 Add strings for Rollouts toggle and update Studies strings

[tomerqodo]

Code Review Bench PR mozilla-mobile#31198

Original PR Title: EXP-5874 Add strings for Rollouts toggle and update Studies strings
Original PR Description: Add Strings for v148, as a base for the split of studies toggle in mozilla-mobile#30988

📜 Tickets

Jira ticket
Bugzilla issue

💡 Description

See mozilla-mobile#30988 for full changes.

📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code

Original PR URL: mozilla-mobile#31198