Add new metrics to count page flushed by background evictor (#1365)

Add two new metrics according to the
neo-technology/neo4j#23748

modules/ROOT/pages/monitoring/metrics/reference.adoc

@@ -213,6 +213,8 @@ By default, database metrics include:
 |<prefix>.page_cache.pins|The total number of page pins executed by the page cache. (counter)
 |<prefix>.page_cache.evictions|The total number of page evictions executed by the page cache. (counter)
 |<prefix>.page_cache.evictions.cooperative|The total number of cooperative page evictions executed by the page cache due to low available pages. (counter)
+|<prefix>.page_cache.eviction.flushes|label:new[Introduced in 5.17]The total number of pages flushed by page eviction. (counter)
+|<prefix>.page_cache.eviction.cooperative.flushes|label:new[Introduced in 5.17]The total number of pages flushed by cooperative page eviction. (counter)
 |<prefix>.page_cache.page_faults|The total number of page faults in the page cache. If this count keeps increasing over time, it may indicate that more page cache is required. However, note that when Neo4j Enterprise starts up, all page cache warmup activities result in page faults. Therefore, it is normal to observe a significant page fault count immediately after startup. (counter)
 |<prefix>.page_cache.page_fault_failures|The total number of failed page faults happened in the page cache. (counter)
 |<prefix>.page_cache.page_cancelled_faults|The total number of cancelled page faults happened in the page cache. (counter)