Add a 5 minute timeout to python tests.

The CI times out after 10 minutes of no output. It's annoying if a
test hangs and is killed by the CI timeout, because you don't get
information about which test was running. Try to avoid that, by adding
a slightly smaller timeout in pytest itself. You can override it on a
per-test basis if needed, but let's try to keep our tests shorter than
that.

For the Postgres regression tests, use a longer 30 minute timeout.
They're not really a single test, but many tests wrapped in a single
pytest test. It's OK for them to run longer in aggregate, each
Postgres test is still fairly short.

pyproject.toml

@@ -24,6 +24,7 @@ moto = {version = "^3.0.0", extras = ["server"]}
 backoff = "^1.11.1"
 pytest-lazy-fixture = "^0.6.3"
 prometheus-client = "^0.14.1"
+pytest-timeout = "^2.1.0"
 
 [tool.poetry.dev-dependencies]
 yapf = "==0.31.0"