Change MAINTAINERS and added CODEOWNERS

[ajnavarro]

Signed-off-by: Antonio Navarro Perez antnavper@gmail.com

• [x] I updated the documentation explaining the new behavior if any.
• [x] I updated CHANGELOG.md file adding the new feature or bug fix.
• [x] I updated go-mysql-server using make upgrade command if applicable.
• [x] I added or updated examples if applicable.
• [x] I checked that changes on schema are reflected into the documentation, if applicable.