Rewrite /cdns/capacity to Go

[ocket8888]

I'm submitting an ...

improvement request (usability, performance, tech debt, etc.)

Traffic Control components affected ...

• Documentation (possibly)
• Traffic Ops

Current behavior:

/cdns/capacity is handled by Perl

Expected / new behavior:

/cdns/capacity should be handled by Go

Minimum API Version

1.1

Request Methods

• GET

Minimal reproduction of the problem with instructions:

N/A

Anything Else

PR in progress: #2306