Adds auto_environment_variable smart attribute

[HazelGrant]

Partially fixes #3081 - Cannot edit auto_environment_variables yet

[johrstrom]

I don't think we need the addition of job_environment here - it should work just like all the other smart attributes.

I think the structure of this is a bit off - like you're doing a lot of the work in this model when a lot of this parsing & updating logic should be embedded in the smart attribute itself.

I.e., it knows how to build itself and apply attributes to it.

So given a YAML like this:

form:
  - auto_environment_variable_FOO
attributes:
  auto_environment_variable_FOO:
    value: bar

That would call the factory method like

#  SmartAttributes::AttributeFactory.build(form_item_id, attrs) evaluates to 
SmartAttributes::AttributeFactory.build('auto_environment_variable_FOO', { value: 'bar' })

Then in the factory - we can do something similar to what auto_modules does - the factory parses out FOO and supplies it as an argument to the builder

ondemand/apps/dashboard/app/lib/smart_attributes/attribute_factory.rb

Lines 13 to 17 in a61aef6

	if id.match?(AUTO_MODULES_REX)
	hpc_mod = id.match(AUTO_MODULES_REX)[1]
	id = 'auto_modules'
	opts = opts.merge({'module' => hpc_mod})
	end