Add benchmarks workflow

[ocelotl]

Fixes #3449

Similar to:

open-telemetry/opentelemetry-js#4144
open-telemetry/opentelemetry-java#5842

For this to work, we also need a few changes:

1. Create a benchmarks branch in this repo.
2. Configure the URL path in Github pages (similar to this).

I tested this in a separate Github organization, here is the corresponding repo. The charts are published here.

open-telemetry/community#1700 tracks the changes needed to run these benchmarks on the open-telemetry Github organization runners.

[ocelotl]

Besides adding this workflow, part of the plan is to create a new orphan branch named benchmarks where there are 2 files. Rendering these files produces charts like these.