Support service resolution

[pleshakov]

This PR introduces ServiceStore component that stores services
and supports resolving service namespace and name into its ClusterIP.

In the future, the component will be extended to support Endpoints.

Example of the output of running the Gateway:

. . .
{Op:1 Host:{Value:cafe.example.com PathRouteGroups:[{Path:/ Routes:[{MatchIdx:0 RuleIdx:0 Source:0xc000407200}]} {Path:/coffee Routes:[{MatchIdx:0 RuleIdx:0 Source:0xc000407500}]} {Path:/tea Routes:[{MatchIdx:0 RuleIdx:0 Source:0xc000124900}]}]}}
Service default/main error: service default/main doesn't exist
Service default/coffee: 10.96.137.50:80
Service default/tea: 10.96.23.88:80
. . .