Should resolve the failure in
https://github.com/coredns/coredns/pull/2541.

This change is breaking to clustering plugin developers (not Caddy
users), but logical, since only the caddytls package uses CertMagic
directly (the httpserver package also uses it, but only because it also
uses the caddytls plugin); and it is early enough that no clustering
plugins really exist yet.

This will also require a change of devportal
so that it looks for a different registration function, which has moved
to the caddytls package.

* optimized parse cli's disabledMetrics flag string to initTelemetry

* add splitTrim to obtain string slice that not contain empty string

* change TestSplitTrim error output

* gofmt for run_test.go

* restore name of disabledMetrics made more sense

* optimized TestSplitTrim case

* just update splitTrim comment to force CI restart

By using option ca_certificates in proxy block it is possible now to select
CA against which backend certificates shall be checked.

Resolves #1550
Co-authored-by: Danny Navarro <navdgo@gmail.com>

* caddytls: Fix empty SNI handling (new -default-sni flag)

vendor: update certmagic, needed to support this

Hopefully fixes #2451, fixes #2438, and fixes #2414

* caddytls: Don't overwrite certmagic Manager (fixes #2407)

Supersedes #2447

* vendor: Update certmagic to fix nil pointer deref and TLS-ALPN cleanup

* Improve -default-sni flag help text

Other methods are not currently implemented in the static file server

* spelling: access

* spelling: associated

* spelling: because

* spelling: characteristics

* spelling: chooses

* spelling: cleared

* spelling: clustering

* spelling: collaborators

* spelling: connection

* spelling: content

* spelling: conversion

* spelling: deferring

* spelling: detection

* spelling: displayed

* spelling: dispenser

* spelling: heuristic

* spelling: nonexistent

* spelling: oflisting

* spelling: preparses

* spelling: response

* spelling: responder

* spelling: sensitive

* spelling: specify

* spelling: simple

* spelling: spawning

* spelling: status

* spelling: unsupported

* spelling: upstream

* spelling: username

* spelling: whether

For log and errors directive, as well as process log.

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