Replace all of Boulder's usage of the Go stdlib "math/rand" package with
the newer "math/rand/v2" package which first became available in go1.22.
This package has an improved API and faster performance across the
board.
See https://go.dev/blog/randv2 and https://go.dev/blog/chacha8rand for
details.
ACME Challenges are well-known strings ("http-01", "dns-01", and
"tlsalpn-01") identifying which kind of challenge should be used
to verify control of a domain. Because they are well-known and
only certain values are valid, it is better to represent them as
something more akin to an enum than as bare strings. This also
improves our ability to ensure that an AcmeChallenge is not
accidentally used as some other kind of string in a different
context. This change also brings them closer in line with the
existing core.AcmeResource and core.OCSPStatus string enums.
Fixes#5009
## CI: restore load-generator run.
This restores running the `load-generator` during CI to make sure it doesn't bitrot. It was previously removed while we debugged the VA getting jammed up and not cleanly shutting down.
Since the global `pebble-challtestsrv` and the `load-generator`'s internal chall test srv will conflict this requires moving the `load-generator` run to the end of integration tests and updating `startservers.py` to allow the load gen integration test code to stop the `pebble-challtestsrv` before starting the `load-generator`.
The `load-generator` and associated config are updated to allow specifying bind addresses for the DNS interface of the internal challtestsrv. Multiple addresses are supported so that the `load-generator`'s chall test srv can listen on port DNS ports Boulder is configured to use. The `load-generator` config now accepts a `fakeDNS` parameter that can be used to specify the default IPv4 address returned by the `load-generator`'s DNS server for A queries.
## load-generator: support different challenges/strategies.
Updates the load-generator to support HTTP-01, DNS-01, and TLS-ALPN-01 challenge response servers. A new challenge selection configuration parameter (`ChallengeStrategy`) can be set to `"http-01"`, `"dns-01"`, or `"tls-alpn-01"` to solve only challenges of that type. Using `"random"` will let the load-generator choose a challenge type randomly.
Resolves https://github.com/letsencrypt/boulder/issues/3900
Aaron Gable
Jacob Hoffman-Andrews
Daniel McCarney