Create a user guide & learning doc for adding benchmark schema templates to new integrations

[lalit-satapathy]

As part of the addition of various benchmark templates for the recent packages there has been various learnings. It will be nice to capture the same in a developer guide here.

Assigning to Aliabbas and me for tracking.

CC: @ruflin @tommyers-elastic @alaudazzi

[ruflin]

Part of it, is improving the existing docs around benchmarks, the other part for me is making improvements to the benchmark command itself. What we can we do make building templates simpler? For example helper for the agent fields etc.?