[rush-serve-plugin] Add build status monitoring via WebSocket

[dmichon-msft]

Summary

Adds a new configuration option buildStatusWebSocketPath to @rushstack/rush-serve-plugin that, when configured, enables a secure web socket server at wss://localhost:${port}${buildStatusWebSocketPath}.

A client can connect a WebSocket at the aforementioned path to receive information about the status of the current watch-mode build command.

Details

Upon connecting a WebSocket to the server, the plugin will send a sync message that lists all current operations and their statuses, the overall status of the build, and some metadata about the current session (the name of the command, the machine the command is running on).

Whenever the status of one or more operations in the build graph changes, a status-change message will be sent with the new states of the affected operations.

Upon completion of the build, an after-execute message will be sent, containing the final aggregate build status.

Future Work

Add support for fetching build logs and streaming log content.

How it was tested

Temporarily connected rush-serve-plugin to be one of the default Rush plugins in start-dev.js.
Configured a global rule to host a static HTML page that connected to the web socket server and monitored for live updates.

Impacted documentation

The list of OperationStatus values in Rush. The package documentation and schema for @rushstack/rush-serve-plugin.