Add MetricsFileDirectory parameter to ScriptExecutor

[Rohit Chaturvedi (rhch1309)]

Description

ScriptExecutor expects the script under execution to emit its metrics as test-metrics.json in the script directory:

this.MetricsFilePath = this.Combine(this.ExecutableDirectory, ScriptExecutor.MetricsFileName);
if (this.fileSystem.File.Exists(this.MetricsFilePath))
{
	this.fileSystem.File.Delete(this.MetricsFilePath);
}

When several Virtual Client instances run concurrently on the same machine against a shared package directory (a common lab/harness setup), every instance resolves the same metrics file path. Each instance then deletes that file during InitializeAsync while clearing stale results, so one experiment can remove the metrics file belonging to another experiment that is mid-run.

There is currently no way to scope the metrics file per instance. LogPaths can already be scoped by supplying a relative prefix, but the metrics path is fixed.

Change

Adds an optional MetricsFileDirectory parameter that supplies a directory path, relative to the script directory, in which the script writes the metrics file:

"MetricsFileDirectory": "{experimentId}"

Since profile parameters are resolved by EvaluateParametersAsync before the path is composed, placeholders such as {experimentId} work as expected, giving each concurrent instance its own metrics file.

Notes on scope:

• The metrics file name is deliberately left unchanged (test-metrics.json), since that is the contract with the script. Only the containing directory is configurable.
• When the parameter is not defined, MetricsFilePath resolves exactly as before, so existing profiles are unaffected.
• No change to log capture, error handling, or cancellation behavior.

The example profile (EXAMPLE-EXECUTE-SCRIPT.json) and the extensions guide are updated to document the parameter.

Validation

• dotnet build src/VirtualClient/VirtualClient.sln -c Debug — succeeds, 0 warnings, 0 errors.
• VirtualClient.Actions.UnitTests filtered to ScriptExecutor — 32/32 passing.
• EXAMPLE-EXECUTE-SCRIPT.json validated as well-formed JSON.

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