Use /admin/v1/register in create-account

[S7evinK]

The create-account utility is updated to use the existing /_synapse/admin/v1/register endpoint, similar to register_new_matrix_user on Synapse. This ensures all needed functions are called to propagate e.g. account data.
Unfortunately, this means "passwordless" accounts can't be created anymore.
Resetting a password still uses a direct database connection.

[neilalexander]

Things like this make me wonder whether we should turn user creation into an admin endpoint instead of having create-account talk to the database directly. I don't really like the fact that we have to create workarounds like this when we should just update the accounts & account data using the built-in APIs and have the stream positions advanced properly.

[genofire]

@neilalexander , i understand you position.

So we should use the same function (of creating accounts) for cmd and URL-Endpoint, without going over the Endpoint ... to prevent missing to create data in the database (for notification or something else).

[McSinyx]

How do I fix accounts created with create-account?