Document new .NET 8 runtime counters (#43017)

Author: tommcdon

docs/core/diagnostics/available-counters.md

@@ -40,6 +40,8 @@ The following counters are published as part of .NET runtime (CoreCLR) and are m
 | :::no-loc text="IL Bytes Jitted"::: (`il-bytes-jitted`) | The total size of ILs that are JIT-compiled, in bytes | .NET 5 |
 | :::no-loc text="Methods Jitted Count"::: (`methods-jitted-count`) | The number of methods that are JIT-compiled | .NET 5 |
 | :::no-loc text="GC Committed Bytes"::: (`gc-committed`) | The number of bytes committed by the GC | .NET 6 |
+| :::no-loc text="Time paused by GC"::: (`total-pause-time-by-gc`) | The total amount of time program execution was paused by the GC | .NET 8 |
+| :::no-loc text="Gen 0 GC Budget"::: (`gen-0-gc-budget`) | The Gen 0 memory budget | .NET 8 |
 
 ## Microsoft.AspNetCore.Hosting counters