ingest benchmark: after effective_io_concurrency = 100 we can increase compute side parallelism (#9904)

## Problem

ingest benchmark tests project migration to Neon involving steps
- COPY relation data
- create indexes
- create constraints

Previously we used only 4 copy jobs, 4 create index jobs and 7
maintenance workers. After increasing effective_io_concurrency on
compute we see that we can sustain more parallelism in the ingest bench

## Summary of changes

Increase copy jobs to 8, create index jobs to 8 and maintenance workers
to 16

test_runner/performance/test_perf_ingest_using_pgcopydb.py

@@ -60,13 +60,13 @@ def build_pgcopydb_command(pgcopydb_filter_file: Path, test_output_dir: Path):
         "--no-acl",
         "--skip-db-properties",
         "--table-jobs",
-        "4",
+        "8",
         "--index-jobs",
-        "4",
+        "8",
         "--restore-jobs",
-        "4",
+        "8",
         "--split-tables-larger-than",
-        "10GB",
+        "5GB",
         "--skip-extensions",
         "--use-copy-binary",
         "--filters",
@@ -136,7 +136,7 @@ def run_command_and_log_output(command, log_file_path: Path):
         "LD_LIBRARY_PATH": f"{os.getenv('PGCOPYDB_LIB_PATH')}:{os.getenv('PG_16_LIB_PATH')}",
         "PGCOPYDB_SOURCE_PGURI": cast(str, os.getenv("BENCHMARK_INGEST_SOURCE_CONNSTR")),
         "PGCOPYDB_TARGET_PGURI": cast(str, os.getenv("BENCHMARK_INGEST_TARGET_CONNSTR")),
-        "PGOPTIONS": "-c maintenance_work_mem=8388608 -c max_parallel_maintenance_workers=7",
+        "PGOPTIONS": "-c maintenance_work_mem=8388608 -c max_parallel_maintenance_workers=16",
     }
     # Combine the current environment with custom variables
     env = os.environ.copy()