Add CI for synapse_port_db (#6140)

This adds:

* a test sqlite database
* a configuration file for the sqlite database
* a configuration file for a postgresql database (using the credentials in `.buildkite/docker-compose.pyXX.pgXX.yaml`)

as well as a new script named `.buildkite/scripts/test_synapse_port_db.sh` that:

1. installs Synapse
2. updates the test sqlite database to the latest schema and runs background updates on it
3. creates an empty postgresql database
4. run the `synapse_port_db` script to migrate the test sqlite database to the empty postgresql database (with coverage)

Step `2` is done via a new script located at `scripts-dev/update_database`.

The test sqlite database is extracted from a SyTest run, so that it can be considered as an actual homeserver's database with actual data in it.

.buildkite/postgres-config.yaml

@@ -0,0 +1,19 @@
+# Configuration file used for testing the 'synapse_port_db' script.
+# Tells the script to connect to the postgresql database that will be available in the
+# CI's Docker setup at the point where this file is considered.
+server_name: "test"
+
+report_stats: false
+
+database:
+  name: "psycopg2"
+  args:
+    user: postgres
+    host: postgres
+    password: postgres
+    database: synapse
+
+# Suppress the key server warning.
+trusted_key_servers:
+  - server_name: "matrix.org"
+suppress_key_server_warning: true

.buildkite/scripts/test_synapse_port_db.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+#
+# Test script for 'synapse_port_db', which creates a virtualenv, installs Synapse along
+# with additional dependencies needed for the test (such as coverage or the PostgreSQL
+# driver), update the schema of the test SQLite database and run background updates on it,
+# create an empty test database in PostgreSQL, then run the 'synapse_port_db' script to
+# test porting the SQLite database to the PostgreSQL database (with coverage).
+
+set -xe
+cd `dirname $0`/../..
+
+# Create a virtualenv and use it.
+virtualenv env
+source env/bin/activate
+
+# Install dependencies for this test.
+pip install psycopg2 coverage coverage-enable-subprocess
+
+# Install Synapse itself. This won't update any libraries.
+pip install -e .
+
+# Make sure the SQLite3 database is using the latest schema and has no pending background update.
+scripts-dev/update_database --database-config .buildkite/sqlite-config.yaml
+
+# Create the PostgreSQL database.
+PGPASSWORD=postgres createdb -h postgres -U postgres synapse
+
+# Run the script
+coverage run scripts/synapse_port_db --sqlite-database .buildkite/test_db.db --postgres-config .buildkite/postgres-config.yaml

.buildkite/sqlite-config.yaml

@@ -0,0 +1,16 @@
+# Configuration file used for testing the 'synapse_port_db' script.
+# Tells the 'update_database' script to connect to the test SQLite database to upgrade its
+# schema and run background updates on it.
+server_name: "test"
+
+report_stats: false
+
+database:
+  name: "sqlite3"
+  args:
+    database: ".buildkite/test_db.db"
+
+# Suppress the key server warning.
+trusted_key_servers:
+  - server_name: "matrix.org"
+suppress_key_server_warning: true