Make site label available to site:list and org:site:list commands

[namespacebrian]

Replicating #2665 on a branch in the main repo.

From #2665:

This PR fixes #1968 and does two things:

Makes the site label available to site:list and org:site:list commands when using the --field/--fields options
Adds the ability to filter by site label using the --filter option: --filter='label*=foo'
org:site:list did not have default fields so I set them to keep the default output the same.

Thanks!

[stevector]

@namespacebrian can we merge now that this is approved?

[jazzsequence]

Needs tests before merge

[pwtyler]

I know I'm the one that asked for stuff to be broken out to more cases— consider whether every assertion still should be in the subsequent filter test or not.

[namespacebrian]

maybe this comment is stale, but the 4 assertions i see below all look reasonable to me, especially considering that none of their arguments include method calls so on the surface it appears that they should all be very computationally inexpensive.