feat(EvaluateVariables): Support complex objects in EvaluateVariables stage

[christopherthielen]

You can create an adhoc spel expression that resolves to a complex object...

... and we will happily expand the entire object.

However, if you try to do the same thing in Evaluate Variables stage, you get an error:

java.lang.IllegalArgumentException: Unable to map context to class com.netflix.spinnaker.orca.pipeline.EvaluateVariablesStage$EvaluateVariablesStageContext
...
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.lang.String` out of START_ARRAY token
 at [Source: UNKNOWN; line: -1, column: -1] (through reference chain: com.netflix.spinnaker.orca.pipeline.EvaluateVariablesStage$EvaluateVariablesStageContext[\"variables\"]

This PR changes Variable type from [ key: string, value: string ] to [key: string, value: object]

[marchello2000]

thanks, surprised this hasn't come up earlier

[cfieber]

This is a good change - I wonder how many people are working around the stringyness of the current implementation elsewhere and if any of those spots might bust as a result

[christopherthielen]

@cfieber If users are currently working around this, they're coercing their expression to a string in Evaluate Expressions stage already. I wouldn't expect this change to break since strings are still supported. Unless I'm overlooking some other possibility...

[emjburns]

Nice! Thanks!