Fix/improve API initialization #64

• add documentation on what is to be done
• currently we emit a warning if a member is created by a token that is not associated with a member - skip this warning for the first member
• review/improve what is logged on initialization and startup

@derMicha Then do we still need #4?

Bootstrapping could look like this:

1. first imported user have to be the oidc admin user (e.g. Digitalhausmeisterei)
2. start import, which fails after keycloak user has been created
3. set password for this user
4. add password to binda_importer keycloak oidc config

Next approach:

1. independent from any CSV files we will create always a binda-importer user with admin rights
2. this user will get a generated password and stored locally
3. for all further binda_importer api requests this user will be used