Execute an OPTIONS call and make sure we receive a valid response
independently of the provided username or password as the
authentication step is ignored

* Do not authenticate OPTIONS calls
* Add test for OPTIONS call

Add header X-Forwarded-Port to preset transparent

Closes #2356

* caddy: move EmitEvent(InstanceStartupEvent, instance)

* caddy: update SupportedEvents

A tls.Config must have Certificates or GetCertificate set, in order to
be accepted by tls.Listen and quic.Listen.

Implement `{when_iso_local}` placeholder

This implements the `{when_iso_local}` placeholder. This is like the
`{when_iso}` placeholder but the output is in the current timezone
rather than UTC.

Resolves #2362

All code relating to a caddytls.Config and setting it up from the
Caddyfile is still intact; only the certificate management-related
code was removed into a separate package.

I don't expect this to build in CI successfully; updating dependencies
and vendor is coming next.

I've also removed the ad-hoc, half-baked storage plugins that we need
to finish making first-class Caddy plugins (they were never documented
anyway). The new certmagic package has a much better storage interface,
and we can finally move toward making a new storage plugin type, but
it shouldn't be configurable in the Caddyfile, I think, since it doesn't
make sense for a Caddy instance to use more than one storage config...

We also have the option of eliminating DNS provider plugins and just
shipping all of lego's DNS providers by using a lego package (the
caddytls/setup.go file has a comment describing how) -- but it doubles
Caddy's binary size by 100% from about 19 MB to around 40 MB...!

Fix `s3browser` plugin name

Thanks to @webprofusion-chrisc for spotting this: https://github.com/mholt/caddy/pull/2383#issuecomment-445432256

Fixes https://github.com/techknowlogick/caddy-s3browser/issues/2

* tls: Add support for the tls-alpn-01 challenge

Also updates lego/acme to latest on master.

TODO: This implementation of the tls-alpn challenge is not yet solvable
in a distributed Caddy cluster like the http challenge is.

* build: Allow building with the race detector

* tls: Support distributed solving of the TLS-ALPN-01 challenge

* Update vendor and add a todo in MITM checker