feat: Add sandbox mode to attributes

[Mansi-mParticle]

Instructions

1. PR target branch should be against development
2. PR title name should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-title-check.yml
3. PR branch prefix should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-branch-check-name.yml

Summary

• Added logic to include the sandbox mode flag in the finalAttributes map.

Testing Plan

• Was this tested locally? If not, explain why.
• Tested with sample app

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• Closes https://go.mparticle.com/work/SQDSDKS-7206

[rmi22186]

this lgtm...but can you add a test?