test_runner: skip more tests using decorator instead of pytest.skip (#9704)

## Problem

Running `pytest.skip(...)` in a test body instead of marking the test
with `@pytest.mark.skipif(...)` makes all fixtures to be initialised,
which is not necessary if the test is going to be skipped anyway.

Also, some tests are unnecessarily skipped (e.g. `test_layer_bloating`
on Postgres 17, or `test_idle_reconnections` at all) or run (e.g.
`test_parse_project_git_version_output_positive` more than on once
configuration) according to comments.

## Summary of changes
- Move `skip_on_postgres` / `xfail_on_postgres` /
`run_only_on_default_postgres` decorators to `fixture.utils`
- Add new `skip_in_debug_build` and `skip_on_ci` decorators
- Replace `pytest.skip(...)` calls with decorators where possible

test_runner/performance/pageserver/pagebench/test_pageserver_max_throughput_getpage_at_latest_lsn.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import json
-import os
 from pathlib import Path
 from typing import TYPE_CHECKING
 
@@ -14,7 +13,7 @@ from fixtures.neon_fixtures import (
     PgBin,
     wait_for_last_flush_lsn,
 )
-from fixtures.utils import get_scale_for_db, humantime_to_ms
+from fixtures.utils import get_scale_for_db, humantime_to_ms, skip_on_ci
 
 from performance.pageserver.util import (
     setup_pageserver_with_tenants,
@@ -38,9 +37,8 @@ if TYPE_CHECKING:
 @pytest.mark.parametrize("pgbench_scale", [get_scale_for_db(200)])
 @pytest.mark.parametrize("n_tenants", [500])
 @pytest.mark.timeout(10000)
-@pytest.mark.skipif(
-    os.getenv("CI", "false") == "true",
-    reason="This test needs lot of resources and should run on dedicated HW, not in github action runners as part of CI",
+@skip_on_ci(
+    "This test needs lot of resources and should run on dedicated HW, not in github action runners as part of CI"
 )
 def test_pageserver_characterize_throughput_with_n_tenants(
     neon_env_builder: NeonEnvBuilder,
@@ -66,9 +64,8 @@ def test_pageserver_characterize_throughput_with_n_tenants(
 @pytest.mark.parametrize("n_clients", [1, 64])
 @pytest.mark.parametrize("n_tenants", [1])
 @pytest.mark.timeout(2400)
-@pytest.mark.skipif(
-    os.getenv("CI", "false") == "true",
-    reason="This test needs lot of resources and should run on dedicated HW, not in github action runners as part of CI",
+@skip_on_ci(
+    "This test needs lot of resources and should run on dedicated HW, not in github action runners as part of CI"
 )
 def test_pageserver_characterize_latencies_with_1_client_and_throughput_with_many_clients_one_tenant(
     neon_env_builder: NeonEnvBuilder,