add cache step

[rarmatei]

Example usage here: https://github.com/nrwl/ocean/pull/3507/files#diff-253f6929b89fdec626cb3baf8e817e3c3d61732f03caf0e81707a1b98132f2f3R63

Read docs usage for usage example: https://github.com/nrwl/nx-cloud-workflows/blob/6d87084462d212fb2e638e544236510d41cd0def/workflow-steps/cache/README.md

Next steps:

• immediate next step is to support conditional restores. If a cache entry is found, the restore step should be skipped. It was not possible in this PR, because we do not support step "outputs" right now.
• we need to package up grpc client and all the proto models into an NPM library that we can expose. This should simplify the step code.
• currently we need to pass BASE_BRANCH manually. We should make an update to the runner to try and infer this automatically.
• fallback keys don't work currently. We need to change the caching service to make it work with partial key prefixes. It's a fun extra optimisation we can make. This will work similar to the restoreKeys in Azure: https://learn.microsoft.com/en-us/azure/devops/pipelines/tasks/reference/cache-v2?view=azure-pipelines
• we need to make the cache immutable. Once a key is written to the cache, nothing should be able to update it.
• we still use env vars for inputs. We should have a more structured way of sending inputs to actions, to reduce the chance of conflicts.