Remove authoring specific parameters

[jeo02]

• Logic left in place just removed it from being a flag passed into the CLI and placed it inside of TestCases.json
• ---repo now lets you pass in the reference to replicate the behavior done inside of authoringSpecRepoOption

[Copilot]

Pull request overview

This PR simplifies the benchmarks CLI by removing authoring-specific CLI flags and moving authoring overrides into per-testcase JSON configuration, while also extending --repo to support optional git ref overrides (e.g., Owner/Repo:branch) for CI/PR benchmarking.

Changes:

• Removed --authoring-spec-repo / --authoring-skill-path CLI options and corresponding discovery plumbing; authoring overrides are now read from JSON test case data.
• Added --repo Owner/Name:ref parsing and a BenchmarkOptions.RefOverrides mechanism, applied during workspace preparation.
• Updated benchmarks README to document new --repo behavior and filtering options.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/README.md	Documents --repo filtering/ref override and adds CI/PR branch override guidance.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Program.cs	Removes authoring flags; adds repo parsing/filtering and passes ref overrides into BenchmarkOptions.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Models/RepoConfig.cs	Adds WithRef() and ParseRepoString() helper for Owner/Name[:ref] parsing.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Models/BenchmarkOptions.cs	Adds RefOverrides to carry ref overrides into execution.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Infrastructure/ScenarioDiscovery.cs	Removes authoring override parameters; always loads authoring scenarios from JSON.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Infrastructure/BenchmarkRunner.cs	Applies ref overrides to the scenario repo before workspace preparation.
tools/azsdk-cli/Azure.Sdk.Tools.Cli.Benchmarks/Infrastructure/AuthoringScenarioLoader.cs	Reads authoringSpecRepo / authoringSkillPath from JSON test cases instead of CLI flags.