[PURR][#2799]Add group reviewer to check and approve newly-created group

[kuang5]

PURR Ticket: https://purr.purdue.edu/support/ticket/2799

Groups is not auto-approved on PURR. We want to get the notification when users create group. Also we want to review the uploaded file to group where the file section is open to anyone to make sure the files meet the accessibility standard.

The changes include:

1. Adding reviewers field to the groups component administrator interface.
2. When reviewers' email addresses are set, sending email to group reviewers when new group is created.
3. If the group file section is open to anyone, sending email to group reviewers when any file is uploaded to such group.

Test procedure:

1. Set the reviewers' email addresses in the Group reviewers field on groups component admin interface.
2. Login on hub, open the group creation page, fill out the fields group id, title, description, who can join, discoverability. On access permissions user interface, set Files to Any Hub visitor. Finish the rest fields and finally click on the Save Group button.
3. The reviewer is expected to receive an email which says that a group is submitted and reviewer need to login on admin interface to review and approve it. Reviewer logs in on the admin interface and approve the project.
4. Visit the newly-created group page, choose Files and upload a file. It is expected that the reviewer is going to receive an email says that the file is uploaded to the group and reviewer needs to review it.
5. Create a group to set Files to Registered Hub users or Group members only, finish the rest setting and finally click the Save Group button to finish the group creation.
6. Reviewer receives email regarding pending approval group and approve it through admin interface. Visit the group page to upload a file, then the reviewer should not receive any email notification this time.

The changes were tested on production and they work as expected.