virtualhost.yaml with remap rules

[serrislew]

V2 of #12669 but including remap.yaml (#12997)

• Resolves to a single virtualhost entry
  • Remap rule logic remains the same. Order ranking still applies (i.e. rules defined first have priority)
  • Virtualhost remap rules have priority. If no remap rule matches or virtualhost is found, existing remap.yaml or .config is then considered
• Virtualhost domains support exact and wildcard (only single left-most "*") matching
• Supports traffic_ctl config reload of single virtualhost entry
  • $ traffic_ctl config reload --virtualhost foo
  • Uses token model reload