fix: Allow kratos to preload secret

[Demonsthere]

Related Issue or Design Document

• Fix Pre-deployed kubernetes secrets will result in a broken kratos configuration #349

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Further comments

[Demonsthere]

@christian-roggia this should be an easy fix, allowing the user to preload the secret.
The secret has 2 required fields: dsn and smtpConnectionURI, as secretsDefault and secretsCookie are not required to be set in order to start kratos.