Improvements from the initial CLI, SQL based installer from EZP-23950.

Improvements

Consider distinguishing initial & site installer

Unlike what we have now that duplicates all data on all installers:

• The initial installer (see Minimal repo) sets up the minimal data the repository requires to operate (root folders, folder/user/user group content types, admin account)
• The site installer is meant to add data, probably using the SPI, to the repository.

Minimal repo, a storage engine concern

Minimal install should be a storage engine concern, initializing a given repository (as we support several repos), to be able to be future proof. Additionally we should specify what a minimal repo implies so installers can reliably append and modify this data set across storage engines and future enhancements to the default minimal data.

Admin account customization

It should be possible to customize the admin user's email and password.

Binary files handling

The installer should make sure files are copied to the right place (var/something, to be discussed), using the currently configured IO handler so install can be done on S3/NFS also, and that the references to these path can be updated in the installed repository data.

Approach

It might be optimal to replace SQL based installation with SPI (or API, but then we need to have access to API w/o permission checks) based one for site installer