Added flask secret value for custom auth

[placerda]

This pull request introduces several changes to the infra directory to integrate KeyVault for managing secrets and to grant necessary access permissions. The most important changes include adding KeyVault parameters and resources, updating the appservice.bicep file to use these parameters, and modifying the main.bicep file to include the new KeyVault module.

KeyVault Integration:

• infra/core/host/appservice.bicep: Added parameters for keyVaultName and flaskSecretName, and defined a new KeyVault resource along with a secret for flaskSecretKey. [1] [2]

Access Permissions:

• infra/main.bicep: Updated the frontEnd module to include keyVaultName and flaskSecretName parameters, and added a new module appserviceKeyVaultAccess to handle access permissions for KeyVault. [1] [2]