Add a concept of grouped sites / central auth to addwiki CLI stuff

[addshore]

From https://phabricator.wikimedia.org/T111695

Currently you can define wikis and users separately (stored as 2 separate lists).
This perhaps needs to change a bit to make working with groups of wikis easier.

pywikibot call these families and we could probably do the same?

The CLI script should allow you to easily add a wikifamily (which would fetch them all from the sitematrix)

as yaml I guess this would be something like the below:

families:
    wikimedia:
        sites:
            enwiki: { url: 'https://en.wikipedia.org/w/api.php' }
            wikidata: { url: 'https://www.wikidata.org/w/api.php' }
        users:
            addshore: { username: addshore, password: fake }
            addbot: { username: addbot, password: fake }
            
sites:
    local: {
        url: 'http://localhost/w/api.php',
        users:
            localadmin: { username: localadmin, password: fake }
    }

defaults:
    family: 'wikimedia'
    site: 'enwiki'
    user: 'addshore'

And a default for something not in a family would be:

defaults:
    site: 'local'
    user: 'localadmin'