[Retention] Make retention go even slower (#25357)

Increases the interval between scanning the documents log for retention from 10 mins -> 30 mins. The number of documents scanned per run was also decreased from `10000` - > `1000`. With these changes, we should be good to rollout retention again on monday.

The changes made since the rollout have been:
- removed `documents_to_delete` which should decrease the load by ~1/3
- cursor on scanned documents instead of deleted documents
- increased time between batches -- should decrease load by ~2/3
- decreased documents scanned -- should decrease load by ~9/10

Let me know if there are any more optimizations we should consider.

GitOrigin-RevId: b9e05b1031b7d33ac72cbce6cb25bcbfb78846b5

Author: jordanhunt22

crates/common/src/knobs.rs

@@ -388,13 +388,13 @@ pub static RETENTION_FAIL_ALL_MULTIPLIER: LazyLock<usize> =
 pub static DOCUMENT_RETENTION_BATCH_INTERVAL_SECONDS: LazyLock<Duration> = LazyLock::new(|| {
     Duration::from_secs(env_config(
         "DOCUMENT_RETENTION_BATCH_INTERVAL_SECONDS",
-        10 * 60,
+        30 * 60,
     ))
 });
 
 /// Maximum scanned documents within a single run for document retention
 pub static DOCUMENT_RETENTION_MAX_SCANNED_DOCUMENTS: LazyLock<usize> =
-    LazyLock::new(|| env_config("DOCUMENT_RETENTION_MAX_SCANNED_DOCUMENTS", 10000));
+    LazyLock::new(|| env_config("DOCUMENT_RETENTION_MAX_SCANNED_DOCUMENTS", 1000));
 
 /// Whether or not we run document retention in dry run mode
 pub static DOCUMENT_RETENTION_DRY_RUN: LazyLock<bool> =