Support standard proxy mode in test-proxy

[scbedd]

First step of #6177

todo:

• Successfully get a recording using the new standard proxy mode
• Ensure existing standard mode fixed everywhere
• Add a couple of tests checking new functionality
• Readme updates
• Respond to PR feedback
• REmove stopUniversal or startUniversal. They're unnecessary given that we have the static configuration accessible from startup.cs
• Fix failing recorded tests

[Copilot]

Pull Request Overview

This PR introduces support for standard proxy mode in the test-proxy tool, enabling it to function as a regular HTTP proxy without requiring special request headers. The implementation adds a new command-line flag --standard-proxy-mode and introduces universal recording endpoints that maintain global recording state instead of requiring session-specific headers.

• Adds --standard-proxy-mode command-line option to enable standard HTTP proxy behavior
• Implements universal recording endpoints (StartUniversal/StopUniversal) for simplified recording management
• Adds middleware to handle absolute-form HTTP proxy requests and route them appropriately based on proxy mode

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
try-proxied-requests.ps1	Updates test script to use standard proxy mode and universal recording endpoints
Startup.cs	Adds proxy configuration management and middleware for handling absolute-form requests
RecordingHandler.cs	Updates URI resolution logic to handle standard proxy requests vs legacy Azure mode
Record.cs	Adds universal recording endpoints and updates request handling for different proxy modes
launchSettings.json	Updates default launch configuration to use standard proxy mode
ServerRecordingConfiguration.cs	New model class defining proxy modes and recording configuration
StartOptions.cs	Adds StandardProxyMode property to command-line options
OptionsGenerator.cs	Adds --standard-proxy-mode command-line option definition