Camera trace metrics extension

See the Perfetto Trace-based metrics doc for an overview of how trace metrics are defined and computed.

Perfetto reserves protobuf field 450 - 499 for local development, and 500 - 1000 for vendor extensions. We allocate the vendor extensions as:

• 500 - 600: Core camera metrics
• 600 - 800: Camera feature metrics
• 800 - 1000: Camera app metrics