Update plan service to work with Accounts

[nora-codecov]

Purpose/Motivation

Gazebo uses PlanService to gate user actions, and can block a user from accessing private repos based on the has_seats_left property on the Org. Plan service is not aware of Accounts - we thought a user on a sales-led plan wouldn't interact with PlanService, that assumption was incorrect.

Links to relevant tickets

codecov/engineering-team#2268

What does this PR do?

Updates PlanService to check for presence of an Account then pull the numbers/settings from the Account rather than the Org for read-only purposes. still no write 🙃

[codecov-notifications]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.14%. Comparing base (d038f2e) to head (ac1eec8).
Report is 4 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##               main       #777   +/-   ##
===========================================
  Coverage   96.14000   96.14000           
===========================================
  Files           812        812           
  Lines         18423      18430    +7     
===========================================
+ Hits          17712      17719    +7     
  Misses          711        711           

Flag	Coverage Δ
unit	91.97% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	91.97% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.