Additions/changes for IBM Inferencing work

[chilanti]

1. Added three optional metadata options as shown in examples/config-multi.yaml:

• x_axis_categorical: true -> forces bar charts to use categories (for concurrency) on the x axis rather than spacing the bars proportionally.
• y_axis_log_scale: true -> Triggers logarithmic scale for the y axis on certain charts (TTFT, etc.) where multiple benchmarks can lead to very disparate y values
• show_xref_charts: true -> shows a scatter chart that plots throughput vs resp time (more charts are in the making)

2. Changed the Request Latency unit of measure for y axis to seconds
3. Added a spinner to signal that rendering is in progress