Allow putting to an image with environment variable updates

[matthewmcnew]

Often pipelines contain information that will get updated with and needs to be applied as an environment variable.

Some examples of this are:

• A pipeline rebuilding tomcat configuration and updating the env var to point at the newest version: BP_TOMCAT_EXT_CONF_URI
• Providing a version to the build to the build as environment variable that comes from the semantic version resource. (kpack itself would use this as we currently hard-code the value.)

- put: some-image
  params:
     environment_variables:
          BP_GO_TARGET: "./cmd/controller"
     environment_variables_file:
          CUSTOM_VERSION: "version-resource/version" 

Then: the build-service image is updated with the provided env variables.

• Is there a better name then environment_variables_file?