[Proposal] POEM: provide array result for all runtime images (#5244)

* POEM support array result

* Add missing runtime

* Apply review comment

Author: ningyougang

proposals/POEM-support-array-result.md

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+# Title
+
+Currently, OpenWhisk supports returning a JSON object only, e.g.
+```shell
+# wsk action invoke hello -r
+{
+    "greeting": "Hello stranger!"
+}
+```
+It is necessary to support returning an array too as an array is also a proper JSON object, e.g.
+```shell
+# wsk action invoke hello-array -r
+[
+    "a",
+    "b"
+]
+```
+The sequence action should be considered support as well.
+
+# Status
+* Current state: In-progress
+* Author(s): @ningyougang
+
+# Summary and Motivation
+
+This POEM proposes a new feature that allows user to write their own action which supports an array result.
+So actions would be able to return a JSON object or an array.
+
+# Proposed changes
+## Openwhisk main repo
+Make controller and invoker support both a JSON object and an array result.
+
+## Runtime repos
+All runtime images should support an array result. e.g.
+
+* nodejs (supports by default)
+* go
+* java
+* python
+* php
+* shell
+* docker
+* ruby
+* dotnet
+* rust
+* swift 
+* deno
+* ballerina
+
+## Openwhisk-cli repo
+* The `wsk` CLI needs to support parsing an array result when executing actions.
+* The `wsk` CLI needs to support parsing an array result when getting activations.