chore(triagebot): enable range-diff and review-changes-since (#16152)

### What does this PR try to resolve?

Enable two new triagebot features, which are already adopted in
rust-lang/rust.

**range-diff**:

Enable comments linking to triagebot range-diff when a PR is rebased
onto a different base commit
Documentation at: https://forge.rust-lang.org/triagebot/range-diff.html

**review-changes-since**:

Adds at the end of a review body a link
to view the changes that happened since the review
Documentation at:
https://forge.rust-lang.org/triagebot/review-changes-since.html

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<!-- TRIAGEBOT_SUMMARY_START -->

### Summary Notes

- [range-diff example
comments](#16152 (comment))
by [weihanglo](https://github.com/weihanglo)
- [review-changes-since example
comments](#16152 (comment))
by [weihanglo](https://github.com/weihanglo)

*Managed by `@rustbot`—see
[help](https://forge.rust-lang.org/triagebot/note.html) for details*

<!-- TRIAGEBOT_SUMMARY_END -->
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Author: epage

triagebot.toml

@@ -37,6 +37,16 @@ label = "O-windows"
 # Documentation at: https://forge.rust-lang.org/triagebot/note.html
 [note]
 
+# Enable comments linking to triagebot range-diff when a PR is rebased
+# onto a different base commit
+# Documentation at: https://forge.rust-lang.org/triagebot/range-diff.html
+[range-diff]
+
+# Adds at the end of a review body a link to view the changes that happened
+# since the review
+# Documentation at: https://forge.rust-lang.org/triagebot/review-changes-since.html
+[review-changes-since]
+
 [merge-conflicts]
 remove = []
 add = ["S-waiting-on-author"]
@@ -52,7 +62,6 @@ warn_non_default_branch = true
 [assign.owners]
 "*" = ["@ehuss", "@epage", "@weihanglo"]
 
-
 [review-submitted]
 reviewed_label = "S-waiting-on-author"
 review_labels = ["S-waiting-on-review"]