Build vstats with pkg script

[AbdelrahmanElawady]

This Improvement request (usability, performance, tech debt, etc.) affects these Traffic Control components:

• Traffic Monitor
• CDN in a Box

Current behavior:

In #7746 vstats is currently under infrastructure directory and is built as part of the cache Dockerfile. There are two structs maintained one in vstats and one in Traffic Monitor.

New behavior:

Move vstats under trafficcontrol/varnish and expose stats struct so TM can use it. Build vstats RPM with pkg script and add it to the cache server to use it.