feat: Admin Management Functionality

[MattDavisRV]

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Describe the change
This change includes functionality to manage your Org via Admin API. This change does not include all endpoints and functionality related to the Admin API. As I have time, and if no one else has added them, I will submit another PR for the missing functionality.

Provide OpenAI documentation link
Admin API Documentation

Describe your solution
Implemented functionality to:

• Manage Admin API Keys
• Manage Organization Invites
• Manage Organization Users
• Manage Projects
• Manage Project Users
• View Organization Costs

Tests
Tests have been created for all functionality added. Test methodology was copied from existing tests in the library.

Additional context
I'm unsure why the Sanity checks are failing, they were locally as well, but unrelated to my changes (jsonschema).

Issue: #XXXX

[codecov]

Codecov Report

Attention: Patch coverage is 68.85246% with 114 lines in your changes missing coverage. Please review.

Project coverage is 83.56%. Comparing base (6181fac) to head (b295cf7).

Files with missing lines	Patch %	Lines
examples/admin_usage/main.go	0.00%	42 Missing ⚠️
admin_invite.go	74.13%	10 Missing and 5 partials ⚠️
admin_project.go	77.27%	10 Missing and 5 partials ⚠️
admin_project_user.go	77.27%	10 Missing and 5 partials ⚠️
admin_key.go	76.00%	8 Missing and 4 partials ⚠️
admin_user.go	76.47%	8 Missing and 4 partials ⚠️
admin_usage.go	90.90%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #953      +/-   ##
==========================================
- Coverage   85.93%   83.56%   -2.38%     
==========================================
  Files          43       50       +7     
  Lines        2268     2634     +366     
==========================================
+ Hits         1949     2201     +252     
- Misses        300      390      +90     
- Partials       19       43      +24     

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[MattDavisRV]

I add additional test cases to get a better coverage of the implementation. I believe this is failing the coverage now due to the example included. I see that other examples do not have test written for them, and I didn't see an obvious way to exclude it from being checked.