Fix/corl 2261 children of rejected comments

[marcushaddon]

What does this PR do?

This PR makes disallows replies to comments that are themselves not rejected, but are descendants of rejected comments.

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

This adds the optional boolean field canRespond to the Comment type, which currently just checks for the presence of a rejectedAncestor field on the comment document, but could be utilized for other reasons to disallow replies.

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

No.

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

n/a

How do I test this PR?

1. create root comment
2. create replies +2 levels deep from a couple of commenters
3. report a middle child as commenter
4. verify that middle child can be responded to
5. reject middle child as admin
6. verify that ancestor of rejected ancestor cannot be replied to in My Profile
7. report and reject root comment
8. verify that ancestors of root comment (so, all) cannot be replied to in My Profile tab as commenter
9. unreject root comment as admin
10. verify that ancestors of root comment (that are not also ancestors of rejected ancestor) can be replied to in Comment Stream AND My Profile tab as commenter
11. verify that ancestors of rejected ancestor (from step 3) reply still cannot be replied to
12. unreject rejected ancestor
13. verify that ancestors of now un-rejected ancestor can be replied to

How do we deploy this PR?

No special considerations should be needed.

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[marcushaddon]

@kabeaty Test has been added!