[Runtime API] Implement /services in Runtime API Server

[arunans23]

This issue is created to track the progress of Runtime API /services implementation.

[VajiraPrabuddhaka]

As per the requirement Runtime API should be capable of listing services available in the k8s cluster that the Runtime API is running and make them available for the Runtime API via exposing an endpoint.

As per the OAS defined in #42 it has following endpoints for service discovery related operations.

• /services - List/search services
• /services/{serviceId} - Get details of a particular service
• /services/{serviceId}/usage - Get usage details for a particular service

We did the initial implementation for above using the client-go library by directly calling k8s API server and accessing services across namespaces.

[VajiraPrabuddhaka]

I will keep this issue open as the E2E testing is not completed and the code review is not done yet.