[Improvement] Use of regex on error messages can be fragile in DorisExceptionConverter.java

### What would you like to be improved?

DorisExceptionConverter.java uses a DATABASE_ALREADY_EXISTS_PATTERN_STRING regex to check error messages for databases that already exist. There are several issues with this and regex can be fragile expensive or even a possible DOS vector

### How should we improve?

If possible improve code to not use regexp for this error condition.