Document and verify the installation of extensions to the API Mediation Layer

[balhar-jakub]

Is your feature request related to a problem? Please describe.
There is a way to install at the moment extensions to the API Mediation Layer. It isn't documented and officially supported.

Describe the solution you'd like
To improve the contributions from outside of the squad we should document and standardize the mechanism. This will also contain the information about how to store the relevant variables and how to use the Zowe tools to install and handle lifecycle including upgrades of the extensions.

• Document the standard
• Create a sample extension
• Figure out how to test it

[balhar-jakub]

We should provide the sample showing how to do this.

[achmelo]

Review how this is done in Zowe, should be done in the same way in API ML.

[petacz]

Hi,
It would be better to have a sample that uses some features from API ML.
This is completely independent code and there are no dependencies on API ML.