Implement Enterprise SCIM - EnterpriseService.ListProvisionedSCIMUsers

[elminster-aom]

Related with #3813

Summary

From REST API endpoints for Enterprise SCIM docs, implements:

• List SCIM provisioned identities for an enterprise, GET /scim/v2/enterprises/{enterprise}/Groups

Other changes

• Fix Enterprise.ListProvisionedSCIMGroups Accept header, set it to application/scim+json
• Correct Enterprise.ListProvisionedSCIMGroups unti test function name

[elminster-aom]

Found an incoherence about the Accept header. While the document states for all endpoints:

Headers
accept string
Setting to application/vnd.github+json is recommended.

Their example endpoints use different values. For example on GET .../Users: -H "Accept: application/scim+json"

Reported to GitHub support and they confirmed that:

The correct header is Accept: application/scim+json.

Fix here for EnterpriseService.ListProvisionedSCIMGroups

TODO

Fix for SCIMService endpoints too.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.42%. Comparing base (ea7dd81) to head (b22b4eb).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3839   +/-   ##
=======================================
  Coverage   92.41%   92.42%           
=======================================
  Files         197      197           
  Lines       14152    14167   +15     
=======================================
+ Hits        13079    13094   +15     
  Misses        884      884           
  Partials      189      189           

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[gmlewis]

Thank you, @elminster-aom!
Just a few tweaks, please, then we should be ready for a second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @alexandear - @zyfy29

[gmlewis]

These omitempty fields should be pointers since they are optional values.

[elminster-aom]

On the previous PR, #discussion_r2524023305; @alexandear recommended this structure for options structures:

go-github/github/github.go

Lines 262 to 288 in 4ed75ac

	type ListCursorOptions struct {
	// For paginated result sets, page of results to retrieve.
	Page string `url:"page,omitempty"`
	// For paginated result sets, the number of results to include per page.
	PerPage int `url:"per_page,omitempty"`
	// For paginated result sets, the number of results per page (max 100), starting from the first matching result.
	// This parameter must not be used in combination with last.
	First int `url:"first,omitempty"`
	// For paginated result sets, the number of results per page (max 100), starting from the last matching result.
	// This parameter must not be used in combination with first.
	Last int `url:"last,omitempty"`
	// A cursor, as given in the Link header. If specified, the query only searches for events after this cursor.
	After string `url:"after,omitempty"`
	// A cursor, as given in the Link header. If specified, the query only searches for events before this cursor.
	Before string `url:"before,omitempty"`
	// A cursor, as given in the Link header. If specified, the query continues the search using this cursor.
	Cursor string `url:"cursor,omitempty"`
	}
	// UploadOptions specifies the parameters to methods that support uploads.
	type UploadOptions struct {