Proxy usernames and passwords with special characters have to be URL-escaped
(#2062). The requests fetcher decodes them, but the Playwright and Puppeteer
fetchers and Browser Steps passed the escaped values to the browser as-is.
The proxy URL, password included, was also logged at DEBUG, the default level.
Add proxy_credentials() and redact_proxy_url() in changedetectionio/proxy_url.py
and use them at those sites, with unit tests.
