Consider consolidating spo site and spo site classic commands

[waldekmastykarz]

We should consider simplifying managing sites and consolidate spo site and spo site classic commands into spo site.

With modern sites being the new default, the distinction between modern and classic sites becomes more of a technical nuisance and leads to confusion. Modern sites are still underpinned by classic sites and all of the classic APIs can be used on modern sites as well. So to keep things simple, we should merge all of the functionality of spo site classic commands into spo site, deprecate classic commands and remove them in v3.

Creating sites might require some extra attention/clarification in the documentation as creating team, communication and classic sites requires different set of options, but it's nothing that we couldn't overcome.

[VelinGeorgiev]

Strongly agree, we should not bother the users with that.

[phillipharding]

Agreed, makes perfect sense and avoids confusion

[waldekmastykarz]

Awesome! I've created a number of issues to track the work: #1492, #1493, #1494 and #1495