AO3-7278 Add open_doors role to invitation find permissions

[not-varram]

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Issue

https://otwarchive.atlassian.net/browse/AO3-7278

Purpose

Adds open_doors role to invitation find permissions so admins with this role can see and use the "Track invitations" form on the "Invite New Users" page.

Testing Instructions

1. Log in as an admin with the open_doors role
2. Navigate to Invitations > Invite New Users
3. Verify the "Track invitations" form is visible
4. Test searching by username, email, and token
5. Verify search results are accessible

Credit

varram (he/him)