Add paths for seal config to cache exceptions. (#21223)

Add paths for seal config to cache exceptions.

Add barrierSealConfigPath and recoverySealConfigPlaintextPath to
cacheExceptionsPaths in order to avoid a race that causes some
nodes to always see a nil value.

changelog/21223.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+core: Do not cache seal configuration to fix a bug that resulted in sporadic auto unseal failures.
+```

sdk/physical/cache.go

@@ -32,6 +32,11 @@ var cacheExceptionsPaths = []string{
 	"sys/expire/",
 	"core/poison-pill",
 	"core/raft/tls",
+
+	// Add barrierSealConfigPath and recoverySealConfigPlaintextPath to the cache
+	// exceptions to avoid unseal errors. See VAULT-17227
+	"core/seal-config",
+	"core/recovery-config",
 }
 
 // CacheRefreshContext returns a context with an added value denoting if the