Documentation: Add fcli variable example of accessing array index

[MikeTheSnowman]

I just learned a trick with fcli variables that I think is pretty neat and should probably include an example in the documentation for this. Apparently, if you have an array/list of entities saved to an fcli variable, you can access a specific element in the array/list by its index.

Take the following example:

First I get a list of artifacts from an application and save the result to an fcli variable called art1:

fcli ssc artifact ls --av 10009 --store art1

The command above may produce a list of artifacts that may look something like this:

 Id   Scan types  Last scan date                 Upload date                    Status
 658  WEBINSPECT  2023-06-16T08:49:01.000+00:00  2023-06-16T08:53:34.283+00:00  PROCESS_COMPLETE
 417  WEBINSPECT  2023-04-27T12:04:31.000+00:00  2023-04-27T12:09:11.692+00:00  PROCESS_COMPLETE
 348  WEBINSPECT  2023-03-24T23:54:41.000+00:00  2023-03-24T23:59:55.154+00:00  PROCESS_COMPLETE
 347  WEBINSPECT  2023-03-24T23:48:40.000+00:00  2023-03-24T23:54:04.530+00:00  PROCESS_COMPLETE
...

Now, if you want to use the art1 variable with an fcli command like fcli ssc artifact get, you can not directly pass in the art1 variable by itself, other wise you'll get an error like this:

$ fcli ssc artifact get ::art1::
Exception in thread "main" org.springframework.expression.spel.SpelEvaluationException: EL1008E: Property or field 'id' cannot be found on object of type 'com.fasterxml.jackson.databind.node.ArrayNode' - maybe not public or not valid?
        at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:222)
        at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:105)
        at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:93)

This obviously doesn't work because we're passing in an array/list of artifacts to the artifact get command. So instead we need to simply pass in the id of one of the entries in the array/list. To do that, we can do something like the following:

$ fcli ssc artifact get ::art1::get(0).id
---
id: 658
artifactType: "FPR"
status: "PROCESS_COMPLETE"
allowDelete: true
allowPurge: false
allowApprove: false
inModifyingStatus: false
uploadDate: "2023-06-16T08:53:34.283+00:00"
...

By using the get() method with the fcli variable, we're able to access a specific index in the array/list.