scrubber: add scan-metadata and hook into integration tests (#5176)

## Problem

- Scrubber's `tidy` command requires presence of a control plane
- Scrubber has no tests at all 

## Summary of changes

- Add re-usable async streams for reading metadata from a bucket
- Add a `scan-metadata` command that reads from those streams and calls
existing `checks.rs` code to validate metadata, then returns a summary
struct for the bucket. Command returns nonzero status if errors are
found.
- Add an `enable_scrub_on_exit()` function to NeonEnvBuilder so that
tests using remote storage can request to have the scrubber run after
they finish
- Enable remote storarge and scrub_on_exit in test_pageserver_restart
and test_pageserver_chaos

This is a "toe in the water" of the overall space of validating the
scrubber. Later, we should:
- Enable scrubbing at end of tests using remote storage by default
- Make the success condition stricter than "no errors": tests should
declare what tenants+timelines they expect to see in the bucket (or
sniff these from the functions tests use to create them) and we should
require that the scrubber reports on these particular tenants/timelines.

The `tidy` command is untouched in this PR, but it should be refactored
later to use similar async streaming interface instead of the current
batch-reading approach (the streams are faster with large buckets), and
to also be covered by some tests.


---------

Co-authored-by: Joonas Koivunen <joonas@neon.tech>
Co-authored-by: Alexander Bayandin <alexander@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
Co-authored-by: Conrad Ludgate <conrad@neon.tech>

pageserver/ctl/src/layer_map_analyzer.rs

@@ -3,6 +3,7 @@
 //! Currently it only analyzes holes, which are regions within the layer range that the layer contains no updates for. In the future it might do more analysis (maybe key quantiles?) but it should never return sensitive data.
 
 use anyhow::Result;
+use pageserver::tenant::{TENANTS_SEGMENT_NAME, TIMELINES_SEGMENT_NAME};
 use std::cmp::Ordering;
 use std::collections::BinaryHeap;
 use std::ops::Range;
@@ -142,12 +143,12 @@ pub(crate) async fn main(cmd: &AnalyzeLayerMapCmd) -> Result<()> {
     let mut total_delta_layers = 0usize;
     let mut total_image_layers = 0usize;
     let mut total_excess_layers = 0usize;
-    for tenant in fs::read_dir(storage_path.join("tenants"))? {
+    for tenant in fs::read_dir(storage_path.join(TENANTS_SEGMENT_NAME))? {
         let tenant = tenant?;
         if !tenant.file_type()?.is_dir() {
             continue;
         }
-        for timeline in fs::read_dir(tenant.path().join("timelines"))? {
+        for timeline in fs::read_dir(tenant.path().join(TIMELINES_SEGMENT_NAME))? {
             let timeline = timeline?;
             if !timeline.file_type()?.is_dir() {
                 continue;

pageserver/ctl/src/layers.rs

@@ -5,6 +5,7 @@ use clap::Subcommand;
 use pageserver::tenant::block_io::BlockCursor;
 use pageserver::tenant::disk_btree::DiskBtreeReader;
 use pageserver::tenant::storage_layer::delta_layer::{BlobRef, Summary};
+use pageserver::tenant::{TENANTS_SEGMENT_NAME, TIMELINES_SEGMENT_NAME};
 use pageserver::{page_cache, virtual_file};
 use pageserver::{
     repository::{Key, KEY_SIZE},
@@ -80,13 +81,13 @@ async fn read_delta_file(path: impl AsRef<Path>) -> Result<()> {
 pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
     match cmd {
         LayerCmd::List { path } => {
-            for tenant in fs::read_dir(path.join("tenants"))? {
+            for tenant in fs::read_dir(path.join(TENANTS_SEGMENT_NAME))? {
                 let tenant = tenant?;
                 if !tenant.file_type()?.is_dir() {
                     continue;
                 }
                 println!("tenant {}", tenant.file_name().to_string_lossy());
-                for timeline in fs::read_dir(tenant.path().join("timelines"))? {
+                for timeline in fs::read_dir(tenant.path().join(TIMELINES_SEGMENT_NAME))? {
                     let timeline = timeline?;
                     if !timeline.file_type()?.is_dir() {
                         continue;
@@ -101,9 +102,9 @@ pub(crate) async fn main(cmd: &LayerCmd) -> Result<()> {
             timeline,
         } => {
             let timeline_path = path
-                .join("tenants")
+                .join(TENANTS_SEGMENT_NAME)
                 .join(tenant)
-                .join("timelines")
+                .join(TIMELINES_SEGMENT_NAME)
                 .join(timeline);
             let mut idx = 0;
             for layer in fs::read_dir(timeline_path)? {