Create ToplingDB backup web panel as a SidePlugin

[rockeet]

ToplingDB has AnyPlugin as a general sideplugin interface. Existing builtin AnyPlugins:

• UserKeyCoder, mainly used for show keys of SST file list, which has derived classes:
  • HexUserKeyCoder, HtmlTextUserKeyCoder, PrettyHexUserKeyCoder, DbBenchUserKeyCoder
• SpawnChildProcess
• ModuleGitInfo
• SysInfoShower

The above AnyPlugin are simple, ToplingDB backup web panel should be much complex.

I've created the toplingdb-backup-panel for this task. It's just getting started, and we welcome contributors to jump in and help build it!

ToplingDB/Makefile need to be changed to auto clone toplingdb-backup-panel as other components such as cspp-memtable(just search cspp-memtable in this Makefile for sample template make script).