"Show children" option for modlog

[dullbananas]

Requirements

• Is this a feature request? For questions or discussions use https://lemmy.ml/c/lemmy_support
• Did you check to see if this issue already exists?
• Is this only a feature request? Do not put multiple feature requests in one issue.
• Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.
• Do you agree to follow the rules in our Code of Conduct?

Is your proposal related to a problem?

When you filter by post_id, you may or may not want items for the post's comments to be included. Also applies to comment_id and community_id.

Describe the solution you'd like.

"Show children" option that includes actions for the child items

Describe alternatives you've considered.

None

Additional context

#4664 (comment)