Cli: make namespace optional to adapt to ListAll operation

[Jeffwan]

Why are these changes needed?

CLi doesn't make corresponding changes when we add ListAll

kuberay/proto/cluster.proto

Lines 48 to 53 in cb75cd0

	// Finds all Clusters in all namespaces. Supports pagination, and sorting on certain fields.
	rpc ListAllClusters(ListAllClustersRequest) returns (ListAllClustersResponse) {
	option (google.api.http) = {
	get: "/apis/v1alpha2/clusters"
	};
	}

We want to make namespace field optional so

1. without namespace -> it will fetch all clusters across multiple namespaces
2. with namespace -> fetch cluster under given namespace

./main template compute list
+------------------------+------------+-----+--------+-----+-----------------+
|          NAME          | NAMESPACE  | CPU | MEMORY | GPU | GPU-ACCELERATOR |
+------------------------+------------+-----+--------+-----+-----------------+
| compute-template-test2 | default    |   1 |      1 |   0 |                 |
| compute-mid            | ray-system |   2 |      2 |   0 |                 |
| compute-template-test  | ray-system |   1 |      1 |   0 |                 |
| test                   | ray-system |   1 |      1 |   0 |                 |
| test-hehe              | ray-system |   1 |      1 |   0 |                 |
+------------------------+------------+-----+--------+-----+-----------------+

./main template compute list --namespace=default
+------------------------+-----------+-----+--------+-----+-----------------+
|          NAME          | NAMESPACE | CPU | MEMORY | GPU | GPU-ACCELERATOR |
+------------------------+-----------+-----+--------+-----+-----------------+
| compute-template-test2 | default   |   1 |      1 |   0 |                 |
+------------------------+-----------+-----+--------+-----+-----------------+

Related issue number

Address #348

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[scarlet25151]

Overall LGTM.