Implements a configurable "migration" policy-selector which reads the preferred_username attribute from
the oidc claims and checks if the uid exists in the ocis-accounts service.
A configurable policy-name can be selected based on the outcome of the check.
Currently the proxy generates certificates on every start for dev purposes. This commit adds an option to make this behaviour configurable.
This also removes the dependency on konnectd`s crypto code and copies it instead, as this library is a first version which is not meant for usage by other services.
A proper cert-generation lib should be added to ocis-pkg instead. Then this code can be refactored to use it.
