Declare the inputs of GenerateAntoraPlaybook more precisely

[wilkinsona]

Many of the task's inputs are currently captured in a Map<String, Object>. When comparing build scans this makes it hard to determine why the task was or was not up-to-date. data is represented as a Value property. When the value differs, all that we're shown is that "Input 'data' is in both builds but values are different". Splitting this input up into several more finely grained inputs will make build scans more useful.