[Bug]: Internal Server Error when requesting a nonexistent page under Python 3.8

[jvstme]

Steps to reproduce

1. Run dstack server under Python 3.8.
2. Open http://localhost:3000/aoaoaooao in the browser.

Actual behaviour

Browser says "Internal Server Error".

Expected behaviour

Browser shows the "Not found" page.

dstack version

master

Server logs

File "/home/jvstme/git/dstack/dstack/src/dstack/_internal/server/app.py", line 243, in custom_http_exception_handler
    importlib.resources.files("dstack._internal.server")
AttributeError: module 'importlib.resources' has no attribute 'files'

Additional information

While Python 3.8 is going to be deprecated soon, importlib.resources had other API changes in recent Python versions, which can be causing deprecation warnings now and errors in the future. To avoid them, I can suggest using the official backport.