combinator/idiom for injecting parameters to invoke an action

[rabbah]

  composer.retain(
    composer.value(slackConfig)),
  ({result, params}) => Object.assign(result, params),
  `/whisk.system/slack/post`)

or

  composer.retain(
    composer.value(watsonTranslateConfig)),
  ({result, params}) => Object.assign(result, params),
  `/whisk.system/watson/languageId`)

to avoid creating bindings, or to override parameters/pass secrets to an app.

[rabbah]

the optional properties allowed for a task are merge, input and output, none of these allow one to easily bind parameters to be passed to the task that's called; could build a new combinator for that, or possibly enhance/modify task so that an additional params field is allowed.

this is to make it easier to pass parameters specific to an action without doing the retain/value/smash described above.

[tardieu]

I added example combinators to TEMPLATES.md along these lines.