Actions - Add required:true to args examples and documentation

[davidferlay]

Observed

• There are actions present in this repo:

➜ ag -g action.yaml | grep -v "\.compose"
example/actions/buildargs/action.yaml
example/actions/envvars/action.yaml
example/actions/extrahosts/action.yaml
example/actions/foundation/software/flatcar/actions/bump/action.yaml
example/actions/integration/application/bus/actions/watch/action.yaml
example/actions/platform/actions/build/action.yaml
example/actions/platform/actions/bump/action.yaml
example/actions/arguments/action.yaml
example/actions/alias/action.yaml
example/plugins/action_embedfs/actions/example1/action.yaml
example/plugins/action_embedfs/actions/example2/action.yaml
example/plugins/action_runtime_plugin/action.yaml

• There is no required attribute defined for their arguments

Expected

• required attribute should be defined for action arguments
• documentation should be updated to mention that attribute