Refactor load testing scripts to support Bash and PowerShell

- Updated README.md to reflect changes in load testing commands and added usage examples for Bash scripts.
- Converted PowerShell load testing scripts to Bash equivalents for better cross-platform compatibility.
- Added new Bash scripts: run-loadtests.sh, summarize-artillery.sh, and summarize-k6.sh to mirror existing PowerShell functionality.
- Updated admin-api.js and ws-chat.yml for consistency and improved performance metrics reporting.
- Enhanced error handling and output formatting in summary scripts for better readability.

scripts/cache-hit-ratio.ps1

@@ -1,8 +1,8 @@
-#!/usr/bin/env pwsh
-$ErrorActionPreference = 'Stop'
-
-$scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
-$nodeScript = Join-Path $scriptDir 'cache-hit-ratio.js'
-
-& node $nodeScript @args
-exit $LASTEXITCODE
+#!/usr/bin/env pwsh
+$ErrorActionPreference = 'Stop'
+
+$scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+$nodeScript = Join-Path $scriptDir 'cache-hit-ratio.js'
+
+& node $nodeScript @args
+exit $LASTEXITCODE