#1669 prosodyctl cert import searches by filename rather than subjectName
Description of feature:
prosodyctl should take advantage of the new indexing feature in certmanager ( https://hg.prosody.im/trunk/rev/c0c859425c22 ) to import certificates from a directory.
This will remove unnecessary warnings about certificates that couldn't be found, if those domains exist in other files (e.g. if example.com.crt is also valid for muc.example.com).
Users are scared and confused by the current behaviour even when it succeeds, and in some scenarios it doesn't succeed when it could.