[chore](cloud) Add show hotspot tablet API on BE

[gavinchou]

Usage:

• Get all tablets {metrics} with descending order curl beip:http_port/api/hotspot/tablet?metrics={metrics}
• Get top n tablets {metrics} with descending order curl beip:http_port/api/hotspot/tablet?metrics={metrics}&topn={n}

"metrics" must be specified, which is one of

• read_block
• write
• compaction
• num_rowsets
• num_cumu_rowsets
• num_base_rowsets

Co-authored-by: plat1ko [email protected]

TODO: Add support for local mode.