Add push notifications for organization members

[anton-bondaronok]

Description

After migrating gems to an organization, members stopped receiving push/yank emails that used to go to personal ownership notifiers. This restores those notifications for confirmed organization members.

Closes #6329

Approach

• Mirror the existing per-gem ownership notifier model with memberships.push_notifier (default true), instead of a shared org-level email field.
• On gem push/yank for an organization-owned gem, email confirmed members with push_notifier enabled.
• Let members toggle the setting on the existing Email notification settings page (Organizations section); the page is also available to users who only have org memberships.
• Include organization rows in the notifiers_changed confirmation email.

Note:
Happy to rework this to the org-level email field approach that was suggested later on the issue, if needed.

---

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.79%. Comparing base (5eaddc9) to head (9f177e5).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6745   +/-   ##
=======================================
  Coverage   97.79%   97.79%           
=======================================
  Files         533      533           
  Lines       11584    11610   +26     
=======================================
+ Hits        11328    11354   +26     
  Misses        256      256           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[brian-penguin]

I think this should cover the problem the org was having around notifications. I am wondering if we still want to have like a freetext comma-separated list of emails on an Org settings page to allow email notifications to go out. I can imagine Organizations might have internal mailing lists that would have an email not associated with a User account

[anton-bondaronok]

@brian-penguin,

Good point! I have thought about it and it might really be useful for some organizations. We could even consider implementing some kind of webhooks to help companies automate some processes. However, for the last point, we need to consider how relevant such needs are to our users and whether it is worth complicating the system.

This PR addresses a specific request from the customer for receiving notifications they have previously received via ownership. As stated on the notification page's description, this is primarily for security reasons.

I believe we can move forward with this solution and return to other automation or improve UX features later if there is a business need for them.

[brian-penguin]

Agreed, I think this fix is good to go independent of any new features in the the org section of the app