[Dev] [DB SIG] Step down as DB SIG maintainer

Hi All,

I'm Bo Zhao, so apologized that I had to step down as DB SIG maintainer today. I worked in openEuler DB SIG for 1 year. SIG partners worked together and made so many great contributions in openEuler. I'm so happy that I can work with you guys. That's an unforgettable time in life.

I will post a PR for the roles removing. Thank you all about your helps and hard work.

openEuler will be better and successful.

Best Regards,

Bo Zhao