Fix up the JavaScript newrelic agent config so it is valid

[LinuxBozo]

Builds on #62 to bring the JavaScript NewRelic agent config in line with Ruby and Python versions.

[cmc333333]

To collect the changes here:

Removed

• monitor_mode: true - no such setting
• transaction_tracer.stack_trace_threshold: 0.5 - no such setting
• transaction_tracer.explain_enabled: true - no such setting
• transaction_tracer.function_trace: - no such setting
• error_collector.enabled: true - default setting
• error_collector.ignore_errors: - no such setting
• browser_monitoring.auto_instrument: true - no such setting
• thread_profiler.enabled: true - no such setting

Added

• agent_enabled: true - not required, as it's the default
• capture_params: false - not required, as it's the default
• transaction_tracer.top_n: 20 - not required, as it's the default

Modified

• transaction_tracer.explain_threshold: 0.5 -> 500 - previous value was invalid; this may not be required as it's the default value

[LinuxBozo]

@cmc333333 Yep, you nailed it. Previous configuration looked like maybe an accidental copy from the Ruby settings. I brought it inline with proper settings, and JS formatting, and yes, while adding some defaults, they are there in case folks might want to tweak them (most common tweaks to make)