les: historical data garbage collection (#19570)

This change introduces garbage collection for the light client. Historical
chain data is deleted periodically. If you want to disable the GC, use
the --light.nopruning flag.

graphql/graphql.go

@@ -584,7 +584,7 @@ func (b *Block) TotalDifficulty(ctx context.Context) (hexutil.Big, error) {
 		}
 		h = header.Hash()
 	}
-	return hexutil.Big(*b.backend.GetTd(h)), nil
+	return hexutil.Big(*b.backend.GetTd(ctx, h)), nil
 }
 
 // BlockNumberArgs encapsulates arguments to accessors that specify a block number.