Add `Set-CCMGroup` Cmdlet

Being able manage CCM Groups from the API is great. Right now we have Add and Remove, which is great for net-new groups, and removal of existing groups.

What we currently lack is maintaining existing groups. Enter `Set-CCMGroup`. This cmdlet would allow a user to pipe data from an external system into this cmdlet, and either Add or Remove group memberships, etc.

Start by reading the existing Add and Remove cmdlets in the ChocoCCM PowerShell module and the API operations they use. Define the supported pipeline input and how membership additions and removals should be represented before implementing Set-CCMGroup. Done means an existing group can be synchronized from external data with both membership changes handled consistently.

Written by the indexing model from the issue text.