Add logging for configuration issues

[fdw]

Describe the bug
We're using Spring Cloud 2020.0.1 with Spring Boot 2.4.2 and the new configuration setup (i.e. spring.config.import=vault://).
When configuring Spring Cloud Vault wrongly (i.e. inaccessible URL or invalid credentials), there is no error message about this. It just fails silently to import the properties.
An error message would reduce the necessary debugging time by a lot.

[M3hdi]

You can have the desired behavior by setting the "spring.cloud.vault.fail-fast" config property to "true".
I think it's better to have the fail fast flag switched on by default, which is not currently the case.

[mp911de]

We're missing a bit of infrastructure to be able to inject logger into SecretLeaseContainer and property sources. I created spring-projects/spring-vault#636 to provide the pre-requisites.

[mp911de]

Closing this one as duplicate of #565.