feat: Add has-seats-left to plan query

[RulaKhaled]

Purpose/Motivation

What is the feature? Why is this being done?
Making it easy for the client to check if a plan has seats left or not.

Links to relevant tickets

codecov/engineering-team#1318

What does this PR do?

Include a brief description of the changes in this PR. Bullet points are your friend.

Notes to Reviewer

Anything to note to the team? Any tips on how to review, or where to start?

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. In 2022 this entity acquired Codecov and as result Sentry is going to need some rights from me in order to utilize my contributions in this PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

[codecov-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.52%. Comparing base (03b5754) to head (2fa3ca6).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #528   +/-   ##
=======================================
  Coverage   91.51%   91.52%           
=======================================
  Files         602      602           
  Lines       16352    16367   +15     
=======================================
+ Hits        14965    14980   +15     
  Misses       1387     1387           

Flag	Coverage Δ
unit	91.52% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	91.52% <100.00%> (+<0.01%)	⬆️

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

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[codecov-public-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.52%. Comparing base (03b5754) to head (2fa3ca6).

✅ All tests successful. No failed tests found ☺️

@@           Coverage Diff           @@
##             main     #528   +/-   ##
=======================================
  Coverage   91.51%   91.52%           
=======================================
  Files         602      602           
  Lines       16352    16367   +15     
=======================================
+ Hits        14965    14980   +15     
  Misses       1387     1387           

Flag	Coverage Δ
unit	91.52% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	91.52% <100.00%> (+<0.01%)	⬆️

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

Files	Coverage Δ
graphql_api/types/plan/plan.py	98.43% <100.00%> (+0.10%)	⬆️
plan/service.py	96.26% <100.00%> (+0.08%)	⬆️
plan/test_plan.py	100.00% <100.00%> (ø)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.80%. Comparing base (03b5754) to head (2fa3ca6).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #528     +/-   ##
=======================================
+ Coverage   95.79   95.80   +0.01     
=======================================
  Files        777     777             
  Lines      17208   17223     +15     
=======================================
+ Hits       16484   16499     +15     
  Misses       724     724             

Flag	Coverage Δ
unit	91.52% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	91.52% <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.