add pagination to GET /api/v1/find endpoint

[paskal]

format=tree pagination provides top-level comments with all replies and returns the last top-level comment as last_comment to be used as offset for the next page. If comments and replies overflow the limit, the one stepping out of the limit will not be returned. If the first comment and its replies after the given offset overflow the limit, it will be returned with all the replies.

format=plain pagination works by providing all comments and returning the last comment as last_comment to be used as offset for the next page.

Requires #1685 to be merged first. Backend part for #782.

[github-actions[bot]]

Pull Request Test Coverage Report for Build 7512258238

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 84.281%

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Totals
Change from base Build 7495000583:	-0.5%
Covered Lines:	5946
Relevant Lines:	7055

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