Give the .NET Product Construction Service ability to read Key Vault secrets

[dkurepa]

The .NET Product Construction Service will need to be able to read KeyVault secrets.
We need to figure out what's the best way to do this, while taking into consideration the local development story.

Currently these two approaches look promising:

• Using the built in ContainerApp secrets (https://learn.microsoft.com/en-us/azure/container-apps/manage-secrets?tabs=azure-portal)
• Using Managed Identities on Staging/Prod and corp accounts for the local development, and accessing the secrets through an API

We'll need to investigate a bit more

[dkurepa]

This issue was resolved in #3189. The PR contains a detailed explanation of the issue resolution