Add AZURE_RESOURCE_GROUP Bicep output

[ggailey777]

The shared article include (functions-mcp-connect-remote.md) references $AZURE_RESOURCE_GROUP in the script to retrieve the MCP system key, but the Bicep template doesn't output it. This causes the script to fail.

Added output AZURE_RESOURCE_GROUP string = rg.name to infra/main.bicep to match the Java repo pattern.

[lilyjma]

@ggailey777 the functions-mcp-connect-remote.md isn't an article in this repo. Can you show me where it is?

Also, I've made all the samples enable built-in MCP auth by default, so there's no need to use the system key anymore. Wherever that article is, it should be updated to call that out.

[ggailey777]

Closing — the shared include (functions-mcp-connect-remote.md) no longer uses the system key script. Built-in MCP auth is now enabled by default in all samples, so AZURE_RESOURCE_GROUP is no longer needed.