Spring Cloud Config Jdbc Repository don't try label main

the Git Repository first try label main then master. the Jdbc Repository only try label master.

Comment From: woshikid

I agree to @ryanjbaxter that main and master doesn't mean much in terms of JDBC. But this issues break the consistency of repository behaviors. The first time I try the Jdbc Repository, I thought the label should be main because it's the default in Git Repository. But I got no results, this confused me.

I don't think it's a good idea to implement a 'retry master' feature in Jdbc Repository. Maybe we should change the default label to main for consistency with Git Repository or keep it to master but we mention this in document.

Comment From: woshikid

I just found there's a default-label property in File System Backend. That make things clear. Shall we do the same on JDBC Backend?