Ability for "create variable" to be non-String value

Issue Summary

At the moment, using the "Create Variable" action with a smart value expression will create a variable as the rendered String representation of the expression.

This means that, for example, you can't branch over a list of items added to a variable such as `{{lookupIssues.assignee.distinct}}`.

There are other places where this would be useful e.g. creating variables to hold objects or lists of objects and then performing other smart value operations on those in later parts of a rule.

Steps to Reproduce

1. Do a "Lookup Issue" action to fetch > 1 issue
2. Log the result of {{lookupIssue.summary.length}}
3. Create a variable of {{lookupIssues.summary}}
4. Log the result of {{myVar.length}}

Expected Results

Both log outputs are the same (e.g. they output a list with each element being the length of the issue summary in the lookup issues result)

Actual Results

The first log output is as expected, but the second simply prints the length of the rendered String representation of lookupIssues.summary

Workaround

The full smart value expression needs to be used everywhere.