Add fboss2 show platform-showtech cli

[huyc-arista]

Summary

This is an initial solution to port platform-showtech source code into fboss2 cli to replace the need of the stand-alone platform-showtech script. The goal is to have cli the outputs identical to current platform-showtech script. Future PRs will add Meru and Darwin platform-specific logic and outputs.

The cli syntax will be:

fboss2 show platform-showtech

and for quite mode:

fboss2 show platform-showtech -q true

Blockers

• Looking for pointers on adding a mock fboss2 cli unit test since this command does not follow typical query clients, thrift-model structure of other fboss2 commands

Testing:

• Manually tested the new cli extension on meru800bia/meru800bfa