Remove members_api_expose_enterprise_users_emails_only feature flag

What does this MR do and why?

Related to #439044 (closed)

This MR removes members_api_expose_enterprise_users_emails_only feature flag. We added this flag to safely roll out the change that stops exposing users emails who are provisioned by the group's SAML or SCIM but are not enterprise users.

The feature flag has been set to true on gprd since Jan 26, 2024. We have not seen any report directly related to this change. I think we can remove this flag now.

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assigned to @bdenkovych

added backend maintenanceremoval typemaintenance labels

Reviewer roulette

Category	Reviewer	Maintainer
backend	@syasonik (UTC-5, 7 hours behind author)	@garyh (UTC-6, 8 hours behind author)

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added groupauthentication label

added devopsgovern sectionsec labels

added feature flag label and removed devopsgovern sectionsec labels

added devopsgovern sectionsec labels

changed milestone to %16.9

changed the description

requested review from @stanhu

E2E Test Result Summary

allure-report-publisher generated test report!

e2e-test-on-gdk: ✅ test report for 29fab1a0

expand test summary

+------------------------------------------------------------------+
|                          suites summary                          |
+-------------+--------+--------+---------+-------+-------+--------+
|             | passed | failed | skipped | flaky | total | result |
+-------------+--------+--------+---------+-------+-------+--------+
| Govern      | 65     | 0      | 1       | 0     | 66    | ✅     |
| Data Stores | 2      | 0      | 0       | 0     | 2     | ✅     |
| Monitor     | 4      | 0      | 0       | 0     | 4     | ✅     |
| Create      | 8      | 0      | 3       | 0     | 11    | ✅     |
| Package     | 0      | 0      | 1       | 0     | 1     | ➖     |
| Plan        | 4      | 0      | 0       | 0     | 4     | ✅     |
+-------------+--------+--------+---------+-------+-------+--------+
| Total       | 83     | 0      | 5       | 0     | 88    | ✅     |
+-------------+--------+--------+---------+-------+-------+--------+

e2e-package-and-test: ❌ test report for 29fab1a0

expand test summary

+------------------------------------------------------------------+
|                          suites summary                          |
+-------------+--------+--------+---------+-------+-------+--------+
|             | passed | failed | skipped | flaky | total | result |
+-------------+--------+--------+---------+-------+-------+--------+
| Govern      | 271    | 0      | 22      | 4     | 293   | ✅     |
| Create      | 145    | 3      | 24      | 4     | 172   | ❌     |
| Data Stores | 4      | 0      | 0       | 0     | 4     | ✅     |
| Monitor     | 8      | 0      | 0       | 0     | 8     | ✅     |
| Plan        | 8      | 0      | 0       | 0     | 8     | ✅     |
| Package     | 0      | 0      | 2       | 0     | 2     | ➖     |
+-------------+--------+--------+---------+-------+-------+--------+
| Total       | 436    | 3      | 48      | 8     | 487   | ❌     |
+-------------+--------+--------+---------+-------+-------+--------+

What do you think about flipping this feature to default_enabled: true for 16.9, wait for more feedback, and then drop the feature flag if we don't hear any customer issues?

removed review request for @stanhu

requested review from @stanhu

approved this merge request

resolved all threads

👋 @stanhu, thanks for approving this merge request.

This is the first time the merge request has been approved. To ensure we don't only run predictive pipelines, and we don't break master, a new pipeline will be started shortly.

Please wait for the pipeline to start before resolving this discussion and set auto-merge for the new pipeline. See merging a merge request for more details.

added pipeline:mr-approved label