* 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