Porting server metadata core API to API v3 Part 2

This adapts server metadata API to v3 tree using the new extension
framework.
Partially implements bp v3-api-core-as-extensions

Change-Id: I2013ef255e00e256899f8048c97c1d6c73b3268f
Merge "Porting server metadata core API to API v3 Part 2"