Having the Django and Flask apps both use the module name "app" makes
the tests order-dependent. If the Django "app" is loaded before the
Flask tests, the latter fail because they try to import "app.main",
which doesn't exist

Maybe there's some other way to avoid this collision by unloading "app"
and still have all the tests pass, but I couldn't find it. Just renaming
them seemed simplest.

importlib.metadata was added in 3.8. Now that we no longer support 3.7,
we can use it directly, rather than using the backported implementation.
(We still need to use the backported version of importlib_resources
until we drop 3.8.)

Remove our bespoke test server management, use pytest-xprocess instead.
Ensures that pytest doesn't hang if a test fails, and that the tests run
correctly in VS Code (maybe also on Windows, still to be determined).

Also fixes a couple of issues identified by pylint.

Add support for the FastAPI framework. Load it automatically when
uvicorn is run with a FastAPI app.

Create a log file by default, messages at INFO and above to it. Provide
the env var APPMAP_DISABLE_LOG_FILE to instead log (at WARNING, by
default) to stderr.