Support webauthn (#17957)

Migrate from U2F to Webauthn

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

vendor/github.com/google/certificate-transparency-go/.gitignore

@@ -0,0 +1,29 @@
+*.iml
+*.swo
+*.swp
+*.tfstate
+*.tfstate.backup
+*~
+/.idea
+/certcheck
+/chainfix
+/coverage.txt
+/createtree
+/crlcheck
+/ctclient
+/ct_server
+/ct_hammer
+/data
+/dumpscts
+/etcdiscover
+/findlog
+/goshawk
+/gosmin
+/gossip_server
+/preloader
+/scanlog
+/sctcheck
+/sctscan
+/trillian_log_server
+/trillian_log_signer
+/trillian.json