feat: updates groups page to show only flex groups for customer

[katrinan029]

Description

Fixes bug on the People Management view that is currently displaying all groups (both flex and budget) to all customers. The behavior we want is to only show flex groups that were created by that customer.

https://2u-internal.atlassian.net/browse/ENT-9913

Testing instructions

1. check out this branch locally and run npm run start:stage
2. visit link https://localhost.stage.edx.org:1991/aj-test-co/admin/people-management and confirm that you do not see any group cards displayed. Ensure that you also do not see any results from this endpoint https://courses.stage.edx.org/enterprise/api/v1/enterprise_group/?enterprise_uuids=e035cce5-24dd-4be4-896d-497157c09a39. Lastly, confirm that there are no flex groups for that customer here https://internal.courses.stage.edx.org/admin/enterprise/enterprisegroup/
3. Repeat the steps above for a second customer (e.g. adam-autoapplied-enterprise)

• https://localhost.stage.edx.org:1991/adam-autoapplied-enterprise/admin/people-management
• https://courses.stage.edx.org/enterprise/api/v1/enterprise_group/?enterprise_uuids=02982884-1f1f-4103-b6d7-3a602c1afcbd
• https://internal.courses.stage.edx.org/admin/enterprise/enterprisegroup/

For all changes

• Ensure adequate tests are in place (or reviewed existing tests cover changes)

Only if submitting a visual change

• Ensure to attach screenshots
• Ensure to have UX team confirm screenshots

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 85.83%. Comparing base (482781d) to head (ba0f6c4).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...anagement/data/hooks/useAllFlexEnterpriseGroups.js	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1384      +/-   ##
==========================================
- Coverage   85.83%   85.83%   -0.01%     
==========================================
  Files         624      624              
  Lines       13635    13642       +7     
  Branches     2850     2860      +10     
==========================================
+ Hits        11703    11709       +6     
- Misses       1862     1863       +1     
  Partials       70       70              

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