Download SLRU segments on demand (#6151)

## Problem

See https://github.com/neondatabase/cloud/issues/8673

## Summary of changes


Download missed SLRU segments from page server

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

trace/src/main.rs

@@ -60,6 +60,7 @@ fn analyze_trace<R: std::io::Read>(mut reader: R) {
         match msg {
             PagestreamFeMessage::Exists(_) => {}
             PagestreamFeMessage::Nblocks(_) => {}
+            PagestreamFeMessage::GetSlruSegment(_) => {}
             PagestreamFeMessage::GetPage(req) => {
                 total += 1;