Redact credentials when displaying URLs (#13333)
This PR redacts credentials in displayed URLs.
It mostly relies on a `redacted_url` function (and where possible
`IndexUrl::redacted`). This is a quick way to prevent leaked credentials
but it's prone to programmer error when adding new trace statements. A
better follow-on would use a `RedactedUrl` type with the appropriate
`Display` implementation. This would allow us to still extract
credentials from the URL while displaying it securely. On the plus side,
the sites where the `redacted_url` function are used serve as easy
signposts for where to use the new type in a future PR.
Closes #1714.
