This PR adds a new `zed_urls` module to the `client` crate.
This module contains functions for constructing URLs to Zed properties,
such as zed.dev.
The URLs produced by this module will respect the server URL set via
settings or the `ZED_SERVER_URL` environment variable. This allows them
to correctly reflect the current environment (such as when testing Zed
against a local collab/zed.dev).
Release Notes:
- N/A
