keep secret value to avoid multiple sync call to the keyvault
Based on investigation around performance tests, get_secret is done synchronously blocking the service until the response get back (in average 90ms). The changes here is to 'pin' the value/secret once fetched to the partitionInfo which is cached for 5 minutes. As further improvement, we could turn this call into an asynchronous one (and then optionality then the pin of secret may no longer be necessary).
In addition, an async lock has been in the fetch partition info since in multiple concurrency several income request can pass and leading to several fetch which will reset the cache and then add to synchronous the secret.