Notifications: show different rejection message for rejected pending comments

[nick-funk]

What does this PR do?

When a comment is in the pending state (not visible stream side due to pre-moderation) and is then rejected, show a slightly different text that indicates it was never visible stream side (does not say it was removed from stream).

These changes will impact:

• commenters
• moderators
• admins
• developers

What changes to the GraphQL/Database Schema does this PR introduce?

Adds a previousStatus field to notifications.

Does this PR introduce any new environment variables or feature flags?

No

If any indexes were added, were they added to INDEXES.md?

None

How do I test this PR?

• post a comment as a commenter
• using an admin/mod, reject the comment
• check the commenter's notifications and see they have a rejected notification saying their comment violated guidelines and was removed
• set a commenter to always premoderate in the community tab
• post a comment as that commenter
• using an admin/mod, reject this comment
• check the commenter's notifications and see that they have a different message that says it violated guidelines, but does not say it was removed from the stream

Were any tests migrated to React Testing Library?

No

How do we deploy this PR?

Merge into epic branch.

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[kabeaty]

Looks good!