refactor: failpoint support (#5033)

- move them to pageserver which is the only dependant on the crate fail
- "move" the exported macro to the new module
- support at init time the same failpoints as runtime

Found while debugging test failures and making tests more repeatable by
allowing "exit" from pageserver start via environment variables. Made
those changes to `test_gc_cutoff.py`.

---------

Co-authored-by: Christian Schwarz <christian@neon.tech>

test_runner/regress/test_gc_cutoff.py

@@ -12,13 +12,8 @@ from fixtures.neon_fixtures import NeonEnvBuilder, PgBin
 # test anyway, so it doesn't need any special attention here.
 @pytest.mark.timeout(600)
 def test_gc_cutoff(neon_env_builder: NeonEnvBuilder, pg_bin: PgBin):
-    env = neon_env_builder.init_start()
-
-    pageserver_http = env.pageserver.http_client()
-
-    # Use aggressive GC and checkpoint settings, so that we also exercise GC during the test
-    tenant_id, _ = env.neon_cli.create_tenant(
-        conf={
+    env = neon_env_builder.init_start(
+        initial_tenant_conf={
             "gc_period": "10 s",
             "gc_horizon": f"{1024 ** 2}",
             "checkpoint_distance": f"{1024 ** 2}",
@@ -29,6 +24,11 @@ def test_gc_cutoff(neon_env_builder: NeonEnvBuilder, pg_bin: PgBin):
             "image_creation_threshold": "2",
         }
     )
+
+    pageserver_http = env.pageserver.http_client()
+
+    # Use aggressive GC and checkpoint settings, so that we also exercise GC during the test
+    tenant_id = env.initial_tenant
     endpoint = env.endpoints.create_start("main", tenant_id=tenant_id)
     connstr = endpoint.connstr(options="-csynchronous_commit=off")
     pg_bin.run_capture(["pgbench", "-i", "-s10", connstr])
@@ -39,5 +39,4 @@ def test_gc_cutoff(neon_env_builder: NeonEnvBuilder, pg_bin: PgBin):
         with pytest.raises(subprocess.SubprocessError):
             pg_bin.run_capture(["pgbench", "-P1", "-N", "-c5", "-T500", "-Mprepared", connstr])
         env.pageserver.stop()
-        env.pageserver.start()
-        pageserver_http.configure_failpoints(("after-timeline-gc-removed-layers", "exit"))
+        env.pageserver.start(extra_env_vars={"FAILPOINTS": "after-timeline-gc-removed-layers=exit"})