feat: forward product custom attributes

[mmustafa-tse]

Summary

• A customer raised an issue that we don't forward product custom attributes to GA4/Firebase, after further investigation, I was able to verify that Google accept mapped custom attributes as mentioned here

Testing Plan

• [Y] Was this tested locally? If not, explain why.
• Unit tested and E2E tested (it takes 24 hours for results to show in Firebase for this case, breakpoints were showing to be forwarded as expected and will double verify tomorrow in GA4 dashboard)

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

• Closes https://go.mparticle.com/work/REPLACEME

[BrandonStalnaker]

LGTM