These task depends on T231586
**Acceptance Criteria:**
[ ] Define route for /revision/{id}/compare/{other}
[ ] Ensure wiring is available to wikidiff2 instance described in T231586
[ ] Define route handler for compare that handles the following:
[ ] Request:
[ ] **Must support** HTTP GET/HEAD **only**
[ ] Request headers:
[ ] **Must support** If-Modified-Since: only if the result set has changed since this date
[ ] **Must support** If-None-Match: only if the result set's etag is different from this
[ ] Response:
[ ] Response **must return** JSON
[ ] Responses JSON must have structure:
```
{
"from": {
"id": 889268680
}
"to": {
"id": 848883822
}
"diff": /* output from wikidiff2 */
}
```
[ ] diff: A diff giving the changes associated with the specified slot role. The diff format may depend on the content handler but is expected to be a JSON diff as generated by wikidiff2_inline_json_diff(). Such a JSON diff is an object with a single top-level key "diff".
[ ] Response headers **must contain**:
[ ] Last-Modified: last time this result set was modified
[ ] ETag: etag for this result set
[ ] Response Statuses
[ ] 200 - OK
[ ] 304 - no change since IMS/INM header
[ ] 400 - from and to IDs are from different pages or content type is not wikitext
[ ] 404 - One or both version IDs don't exist