Eventing: need REST/CLI api to update just the "appcode":

Customers are creating CI CD pipelines that automate the Eventing Life Cycle.  Currently we can NOT update just the Function's JavaScript code (like we can settings) as such the user is typically forced to use the UI. (*3)

Consider a pipeline as follows:

1. Take an export Eventing function <function_name>.json from a "dev" environment that may have different settings or bindings (bucket aliases and URL aliases).
2. Pause a "prod" environment <function_name>
3. Update just the "appcode": (nothing else) with JavaScript from step 1.
4. Resume the "prod" environment <function_name>

Item 3. above is what we currently do not have and need a REST API.

(*3) Note customers can currently use something like the example sh script  "ci_cd_update_appcode.sh" attached to CBSE-8863 where the script performs grep and sed operations to so the "appcode": substitution to achieve step 3. above.

In addition we should consider a -wait flag when doing a deploy undeploy pause or resume this would also simplify scripting CI/CD pipelines.