This PR refactors object layer handling such
that upon failure in sub-system initialization
server reaches a stage of safe-mode operation
wherein only certain API operations are enabled
and available.
This allows for fixing many scenarios such as
- incorrect configuration in vault, etcd,
notification targets
- missing files, incomplete config migrations
unable to read encrypted content etc
- any other issues related to notification,
policies, lifecycle etc
This commit adds a unit test for the vault
config verification (which covers also `IsEmpty()`).
Vault-related code is hard to test with unit tests
since a Vault service would be necessary. Therefore
this commit only adds tests for a fraction of the code.
Fixes#7409
