RegionServer Canary can should use Scan just like Region Canary with option to enable Raw Scan

While working on HBASE-28204 to improve Region Canary, It came to notice that RegionServer canary uses the same code as Region Canary to check if a region is accessible. Plus RegionSever Canary doesn't have Raw Scan enabled. 

This JIRA aims to enable Raw Scan option for RegionServer Canary and use Scan only just like Region Canary.