For situations where you want the Vault agent to handle one or more templates but do not require the acquired credentials elsewhere.
Modify the logic in SyncServer so that if there are no sinks, ignore any new credentials. Since SyncServer is responsible for shutting down the agent, make sure it still properly shuts down in this new situation.
Solves #7988
* Simplify Run(): the function that was being sent over a channel doesn't
need to close over anything except latestToken, and we don't need to
create a new one each iteration. Instead just pass the relevant items,
namely the token and sink to work on.
* Disallow the following config combinations:
1. auto_auth.method.wrap_ttl > 0 and multiple file sinks
2. auto_auth.method.wrap_ttl > 0 and single file sink with wrap_ttl > 0
3. auto_auth.method.wrap_ttl > 0 and cache.use_auto_auth_token = true
* Expose errors that occur when APIProxy is forwarding request to Vault.
* Fix merge issues.
* agent/caching: enable caching of leases generated by autoauth token
* add test for auth/token/create path
* update error message log
* Some minor updates
* add sleep timer for renewal logic to process
* Properly compute auto-auth token
* Use inmem sink to track auto-auth token
* update debug statement
* Only add inmem sink if using auto-auth token is allowed
The result will still pass gofmtcheck and won't trigger additional
changes if someone isn't using goimports, but it will avoid the
piecemeal imports changes we've been seeing.
This allows it to authenticate once, then exit once all sinks have
reported success. Useful for things like an init container vs. a
sidecard container.
Also adds command-level testing of it.
