[Story] Verify that all services that can, also use MSI instead of SPN/keys, etc.

[deniscep]

Currently the API uses an API key STATE_STORE_KEY to authenticate against Cosmos DB.
Docker images are also pulled with docker registry credentials instead of MSI.

Desired outcome:

• API uses MSI to authenticate to CosmosDB
• Runner uses MSI to authenticate to ACR

Acceptance critiera

• [Task] API to use Managed Identity to authenticate against Cosmos DB #345 API to use Managed Identity to authenticate against Cosmos DB
• [Task] Verify docker credentials are not passed/stored #575 Runner to pull docker images with Managed Identity