issue: #28960 [milvus-proto
#212](https://github.com/milvus-io/milvus-proto/issues/212)
add new configuration: builtinRoles
user can define roles in config file: `milvus.yaml`
there is an example:
1. db_ro, only have read privileges, include load
2. db_rw, read and write privileges, include create/drop/rename
collection
3. db_admin, not only read and write privileges, but also user
administration
Signed-off-by: PowderLi <min.li@zilliz.com>
