PLT-2077 Support CJK hashtags (#4555)

* Add Korean character ranges to exist CJK pattern

* Add constant for CJK hashtags
Becuase most of keywords in CJK are two characters

* Add CJK ranges to hashtag pattern to handle it.

* Fixes hashtag pattern to apply numbers at last

* Remove a wrong test case
`test_` shouldn't be a hashtag

* Fix hashtag regex to support standard unicodes

* Remove wrong escapes from regex

model/utils.go

@@ -304,7 +304,7 @@ func Etag(parts ...interface{}) string {
 	return etag
 }
 
-var validHashtag = regexp.MustCompile(`^(#[A-Za-zäöüÄÖÜß]+[A-Za-z0-9äöüÄÖÜß_\-]*[A-Za-z0-9äöüÄÖÜß])$`)
+var validHashtag = regexp.MustCompile(`^(#\pL[\pL\d\-_.]*[\pL\d])$`)
 var puncStart = regexp.MustCompile(`^[^\pL\d\s#]+`)
 var hashtagStart = regexp.MustCompile(`^#{2,}`)
 var puncEnd = regexp.MustCompile(`[^\pL\d\s]+$`)