Make provisioning optional

Is your feature request related to a problem? Please describe.

This feature request is related to unwanted behaviours of provisioned accounts:

• not being able to add aliase, see #4964
• no possibility to delete the provisioned account (not everybody wants this)

Describe the solution you'd like

Instead of automatic provisioning, make it optional and use it only as config template (thus, do not treat them differently to manually added accounts). This would allow specifying templates for account config parameters without automatically provisioning them.

Let's say your users often have a nextcloud, m365 and google account with custom but homogenious account parameters (user names, addresses, security, etc). As soon as the user adds an account with matching email, the correct config would be created. Additionally (because provisioned accounts are not treated specially), it would solve #4964

Describe alternatives you've considered

I deleted provisioning altogether because:

• not every user wants to add all accounts. As a consequence, it is more difficult for users to add their accounts.
• because #4964 prevents my users from using aliases

Additional context

No response

No files, tests, or entry points are named. Start by tracing the existing account-provisioning flow and its handling of manually added accounts; done means provisioning can be disabled, configured accounts act as templates, matching accounts receive the configuration, and provisioned accounts support the same operations as manual accounts.