Add storage location to key vault config

[mthalman]

The key vault config is misconfigured because it is missing storageLocation. Without this, it causes the following error when running secret-manager on this config file:

error : Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.DncEng.SecretManager.SecretManifest.CreateStorage(Storage data) in /_/src/SecretManager/Microsoft.DncEng.SecretManager/SecretManifest.cs:line 96

This fixes it by adding the appropriate config to target SourceBuildKeyVault.

[ellahathaway]

Disabling auto-merge; I discovered that the PAT is not stored in our source-build keyvault but in dnceng-pipeline-secrets keyvault. Before making this change, we need to either 1) move our variable groups into our source-build keyvault and re-configure the service connection we use or 2) continue to ask FR for help when rotating this secret.

[ellahathaway]

Also - the source-build bot PATs are currently being managed by the release team via their secret-management pipeline. I suppose the question now is whose responsibility it is to manage these secrets.