Run data loader performance benchmarks after each PR merge

[fordN]

Let's try running our data loader performance benchmarks upon merging of each successful pull request. To save results we can simply post the JSON results file as a comment on the PR.

Plan

• Add new GitHub Actions workflow: benchmark
  • Trigger on PR merge to main
  • Run data loader benchmarks and output prettified results to actions variable or to file
  • Post a comment to the PR with the benchmark results summary and details
• Test the new workflow by temporarily setting a weaker trigger and triggering it