Adding llcreader ASTE model on TACC featuring snapshots

[mgoldberg10]

@antnguyen13 copied ASTE Release 1 output to TACC's Corral and included snapshot diagnostics for users interested in budget closures. This PR makes that model available through llcreader. I copied the structure of #231's CRIOSPortalASTE270Model hosted on AWS.

I added the snapshot diagnostic names to package_state_variables but am open to moving it to its own dictionary.

I found I had to update two lines in llcmodel as well in order to access the existing llcreader ASTE models.

Added some unit tests, updated docs.

[IvanaEscobar]

@mjlosch , this PR needs approval from a maintainer (you) to check CI via GitHub.

@mgoldberg10 , were you able to produce passing tests for the new ASTE access via test_llcreader on your local machine?

[mgoldberg10]

@mjlosch , this PR needs approval from a maintainer (you) to check CI via GitHub.

@mgoldberg10 , were you able to produce passing tests for the new ASTE access via test_llcreader on your local machine?

Yes I got the test_llcreader tests to pass on my machine.

[mjlosch]

@mgoldberg10 Do you think this is ready to be merged?

[mgoldberg10]

@mgoldberg10 Do you think this is ready to be merged?

@mjlosch I encountered some github CI failures along the way but believe I have them resolved. One of them is independent of my additions on this branch, so I am going to make a separate pull request. Once that is merged, I will circle back on this PR.