Feature: Deploy the portal with a Key Vault

**Is your feature request related to a problem? Please describe.**
Currently, secrets (credentials, connection strings...) and configurations are set directly on portal web app components

**Describe the solution you'd like**
A keyvault should be deployed with the portal:
- [ ] The deployment should create a keyvault
- [ ] The deployment should also create all portal secrets (credentials, connection strings, configurations...)
- [ ] The deployment should give read/list permission on secrets to the portal web app component
- [ ] The deployment should set/update each application setting/connections settings of the web app component with keyvault references

**Additional context**
Related to #1661

No file, test, or deployment entry point is named in the issue. Start by locating the portal's Azure deployment configuration and reviewing related issue #1661; done means the deployment creates the Key Vault and secrets, grants the web app read/list access, and uses Key Vault references for application and connection settings.

Written by the indexing model from the issue text.