Setup CI/CD pipeline with PROW to build the code and run unit tests

[gvbalaji]

We need to setup CI/CD pipeline to set up the following tasks for the code repositories.

TODO

• [x] #3
• [x] #4

[radoslawc]

Both code build and unit tests pipelines are now in place and serving PRs. PROW configuration available at: https://github.com/nephio-project/test-infra