MM-52532: Fix golangci warnings (#23709)

https://mattermost.atlassian.net/browse/MM-52532

- Replace golint with revive
- Add makezero linter
- Fix all the required linter failures

Some issues in enterprise and public modules
are yet to be fixed. We send this to expediate things.

server/channels/app/command.go

@@ -811,10 +811,10 @@ func possibleAtMentions(message string) []string {
 // is a special character for usernames (dot, dash or underscore). If not, it
 // returns the same string.
 func trimUsernameSpecialChar(word string) (string, bool) {
-	len := len(word)
+	l := len(word)
 
-	if len > 0 && strings.LastIndexAny(word, usernameSpecialChars) == (len-1) {
-		return word[:len-1], true
+	if l > 0 && strings.LastIndexAny(word, usernameSpecialChars) == (l-1) {
+		return word[:l-1], true
 	}
 
 	return word, false