make the build easier for people building from source

[pjfanning]

There are build details on the project README. People who want to build pekko-management can also look at the .github/workflows directory to get an idea of how the CI builds run.

All the same, with us having to produce source distributions for ASF release compliance and the idea the even git users might clone the repo and look to get the build done locally - we probably need to look at documenting more about the build.

Also, there is probably scope to make the build easier.

The integration tests are the hardest bit to run.

[samueleresca]

I tried to build the project locally and run tests. Few notes after following the "Running the build" section of the README:

• sbt compile and sbt +compile effectively work without particular prerequisites
• Tests KubernetesApiIntegrationTest and LeaseContentionSpec require K8s API Server running and the test fails
• Integration tests run .sh scripts for creating resources in the running cluster.

I would like to proceed as follows:

• Adding the K8s API Server prerequisite specifying that is needed for running the integration tests
• Adding the prerequisite sbt task for setting up the cluster for integration tests
• Documenting everything in the build from sources