Fix TODO comments in aca-foundry-managed-identity docs

[joshfree]

Regarding mcp/servers/Azure.Mcp.Server/azd-templates/aca-foundry-managed-identity at main · microsoft/mcp

1. there's still a "TODO" or two comment in the markdown file
2. We should update both docs to have manual instructions too for customers who can't use AZD. Just like how our root README.md does for people who can't/won't use a VSIX