(test) chore: split out backends

[atarashansky]

Reason for Change

• #TICKET_NUMBER
• If the reason for this PR's code changes are not clear in the issue, state value/impact

Changes

• add
• remove
• modify

Testing steps

• Either list QA steps or reasoning you feel QA is unnecessary
• Describe how you made sure to know that your changes worked. Should allow someone else to go verify your code without in depth knowledge.
• "Unit tested only", "tested in rdev by a, b, c, verifying feature worked by... ", "manually ran pipeline locally with these results: ..."

Checklist 🛎️

• Add product, design, and eng as reviewers for rdev review
• For UI changes, add screenshots/videos, so the reviewers know what you expect them to see
• For UI changes, add e2e tests to prevent regressions
• For UI changes, verify impacted analytics events still work

Notes for Reviewer

[github-actions]

Deployment Summary

• backend_url: https://pr-7127-backend.rdev.single-cell.czi.technology
• backend_de_url: https://pr-7127-backend-de.rdev.single-cell.czi.technology
• backend_wmg_url: https://pr-7127-backend-wmg.rdev.single-cell.czi.technology
• frontend_url: https://pr-7127-frontend.rdev.single-cell.czi.technology
• delete_db_task_definition_arn: arn:aws:ecs:us-west-2:***:task-definition/dp-rdev-pr-7127-deletion:1
• migrate_db_task_definition_arn: arn:aws:ecs:us-west-2:***:task-definition/dp-rdev-pr-7127-migration:1

[codecov]

Codecov Report

Attention: Patch coverage is 95.14563% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 92.64%. Comparing base (e00ff78) to head (9ae547b).
Report is 2 commits behind head on main.

Files	Patch %	Lines
backend/common/server/datadog.py	80.00%	2 Missing ⚠️
backend/common/server/config.py	98.68%	1 Missing ⚠️
backend/de/server/app.py	75.00%	1 Missing ⚠️
backend/wmg/server/app.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7127      +/-   ##
==========================================
+ Coverage   92.50%   92.64%   +0.14%     
==========================================
  Files         185      188       +3     
  Lines       15735    15710      -25     
==========================================
- Hits        14555    14554       -1     
+ Misses       1180     1156      -24     

Flag	Coverage Δ
unittests	92.64% <95.14%> (+0.14%)	⬆️

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