Support running the pallet benchmarks analysis without running the benchmarks

[koute]

This PR adds a new argument to the benchmarking CLI: --json-input <path.json>.

The idea is: you run the benchmarks once and generate raw results with --json-file, and then you can rerun the analysis and regenerate the weights as many times as you want, without actually rerunning the benchmarks.

This is in particular useful when working on the code responsible for the analysis since it makes it possible to do apples-to-apples comparisons while keeping the raw benchmark numbers constant.

Implementation notes

I've decided to just add an extra argument instead of a new command/subcommand since that seemed to be the least intrusive way to introduce this functionality, and there is already a precedent for it in the form of the --list argument; conceptually this might not be the cleanest, but should still be cheap to maintain and doesn't require rewriting half of the code.

I'm also open to suggestions in case someone has a better name for the command line argument. (:

[shawntabrizi]

dont have suggestions about naming or anything like that, but yeah, like the feature

[koute]

@ggwpez Applied your two suggestions; should be good to go!

[ggwpez]

Works perfectly, thanks!

[ggwpez]

/cmd queue -c fmt $ 1

[command-bot]

@ggwpez https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/1892322 was started for your command "$PIPELINE_SCRIPTS_DIR/fmt.sh" 1. Check out https://gitlab.parity.io/parity/mirrors/substrate/-/pipelines?page=1&scope=all&username=group_605_bot to know what else is being executed currently.

Comment /cmd cancel 84-bbfe4e88-014f-4979-be48-7f1563b34be2 to cancel this command or /cmd cancel to cancel all commands in this pull request.

[command-bot]

@ggwpez Command "$PIPELINE_SCRIPTS_DIR/fmt.sh" 1 has finished. Result: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/1892322 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/1892322/artifacts/download.

[koute]

@ggwpez The zip file which the bot generated is empty; is this what you expected? (:

[ggwpez]

bot merge

[ggwpez]

The zip file which the bot generated is empty; is this what you expected? (:

That was just the formatting bot. No idea why it also produces empty zip files 🤷‍♂️ @koute

[Polkadot-Forum]

This pull request has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/polkadot-release-analysis/1026/2

[lisa-parity]

polkadot-developers/substrate-docs#1621
Doc update:
| json-input <json-input-file> | Specifies the path to a JSON file with previously-generated benchmark results. This option enables you to reuse the benchmarks raw results generated with the --json-file to rerun the benchmark analysis and to regenerate the weights for a pallet without actually rerunning the benchmarks tests.