Create new code paths for multiple subsystems in the code. This will
make maintaing this easier later.
Also introduce bugLogIf() for errors that should not happen in the first
place.
This change adds a `Secret` property to `HelpKV` to identify secrets
like passwords and auth tokens that should not be revealed by the server
in its configuration fetching APIs. Configuration reporting APIs now do
not return secrets.
- Adds an STS API `AssumeRoleWithCustomToken` that can be used to
authenticate via the Id. Mgmt. Plugin.
- Adds a sample identity manager plugin implementation
- Add doc for plugin and STS API
- Add an example program using go SDK for AssumeRoleWithCustomToken