compute_ctl: catalog API endpoints (#7575)

## Problem

There are two cloud's features that require extra compute endpoints.

1. We are running pg_dump to get DB schemas. Currently, we are using a
special service for this. But it would be great to execute pg_dump in an
isolated environment. And we already have such an environment, it's our
compute! And likely enough pg_dump already exists there too! (see
https://github.com/neondatabase/cloud/issues/11644#issuecomment-2084617832)
2. We need to have a way to get databases and roles from compute after
time travel (see https://github.com/neondatabase/cloud/issues/12109)

## Summary of changes

It adds two API endpoints to compute_ctl HTTP API that target both of
the aforementioned cases.

---------

Co-authored-by: Tristan Partin <tristan@neon.tech>

test_runner/fixtures/endpoint/http.py

@@ -0,0 +1,23 @@
+import requests
+from requests.adapters import HTTPAdapter
+
+
+class EndpointHttpClient(requests.Session):
+    def __init__(
+        self,
+        port: int,
+    ):
+        super().__init__()
+        self.port = port
+
+        self.mount("http://", HTTPAdapter())
+
+    def dbs_and_roles(self):
+        res = self.get(f"http://localhost:{self.port}/dbs_and_roles")
+        res.raise_for_status()
+        return res.json()
+
+    def database_schema(self, database: str):
+        res = self.get(f"http://localhost:{self.port}/database_schema?database={database}")
+        res.raise_for_status()
+        return res.text

test_runner/fixtures/neon_fixtures.py

@@ -48,6 +48,7 @@ from urllib3.util.retry import Retry
 from fixtures import overlayfs
 from fixtures.broker import NeonBroker
 from fixtures.common_types import Lsn, TenantId, TenantShardId, TimelineId
+from fixtures.endpoint.http import EndpointHttpClient
 from fixtures.log_helper import log
 from fixtures.metrics import Metrics, MetricsGetter, parse_metrics
 from fixtures.pageserver.allowed_errors import (
@@ -3373,6 +3374,13 @@ class Endpoint(PgProtocol):
         self.active_safekeepers: List[int] = list(map(lambda sk: sk.id, env.safekeepers))
         # path to conf is <repo_dir>/endpoints/<endpoint_id>/pgdata/postgresql.conf
 
+    def http_client(
+        self, auth_token: Optional[str] = None, retries: Optional[Retry] = None
+    ) -> EndpointHttpClient:
+        return EndpointHttpClient(
+            port=self.http_port,
+        )
+
     def create(
         self,
         branch_name: str,

test_runner/regress/test_compute_catalog.py

@@ -0,0 +1,34 @@
+import requests
+from fixtures.neon_fixtures import NeonEnv
+
+
+def test_compute_catalog(neon_simple_env: NeonEnv):
+    env = neon_simple_env
+    env.neon_cli.create_branch("test_config", "empty")
+
+    endpoint = env.endpoints.create_start("test_config", config_lines=["log_min_messages=debug1"])
+    client = endpoint.http_client()
+
+    objects = client.dbs_and_roles()
+
+    # Assert that 'cloud_admin' role exists in the 'roles' list
+    assert any(
+        role["name"] == "cloud_admin" for role in objects["roles"]
+    ), "The 'cloud_admin' role is missing"
+
+    # Assert that 'postgres' database exists in the 'databases' list
+    assert any(
+        db["name"] == "postgres" for db in objects["databases"]
+    ), "The 'postgres' database is missing"
+
+    ddl = client.database_schema(database="postgres")
+
+    assert "-- PostgreSQL database dump" in ddl
+
+    try:
+        client.database_schema(database="nonexistentdb")
+        raise AssertionError("Expected HTTPError was not raised")
+    except requests.exceptions.HTTPError as e:
+        assert (
+            e.response.status_code == 404
+        ), f"Expected 404 status code, but got {e.response.status_code}"