Abstracts elections-phragmen pallet to use NposSolver (v2)

[gpestana]

This PR refactors the current elections-phragmen pallet to use an NposSolver instead of hardcoding one flavor of phragmen. In addition, it implements an approval voting election scheme where each voter backs a limited set of candidates, without requiring splitting the stake among the selected candidates.

When using the pallet-elections, one should consider switching to a simpler NposSolver type like the approvals voting scheme, which is lighter than phragmen and reasonable in most cases. Users of this pallet should keep in mind that the election happens periodically on_initialize, and thus ensure that the election weight fits within a block (there is an integrity test to ensure the runtime configs comply).

Note that, although this PR renamed the old pallet-elections-phragmen to pallet-elections, the pallet name in the runtimes did not change in order to avoid a runtime upgrade (we could use move_pallet but that's not recommended). Otherwise a runtime upgrade would have been required.

Finally, this PR removes the need for a separate benchmarking crate for elections-provider-support. This way, it is possible to use the CI bench bot to correctly calculate and commit weights (all changes related to this merged and more info about it in this PR #13431).

polkadot companion: paritytech/polkadot#6278

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs.
Job name: test-linux-stable
Logs: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2624761

[gpestana]

bot bench $ pallet dev pallet-elections

[command-bot]

@gpestana https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756664 was started for your command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" pallet dev pallet-elections. 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 bot cancel 5-d57a451a-08d1-438a-83fa-24d33d047ba7 to cancel this command or bot cancel to cancel all commands in this pull request.

[command-bot]

@gpestana Command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" pallet dev pallet-elections has finished. Result: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756664 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756664/artifacts/download.

[gpestana]

bot bench $ pallet dev frame-election-provider-support

[command-bot]

@gpestana https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756843 was started for your command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" pallet dev frame-election-provider-support. 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 bot cancel 7-00bffb62-38d7-4fd8-9483-7e47e57b0164 to cancel this command or bot cancel to cancel all commands in this pull request.

[command-bot]

@gpestana Command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" pallet dev frame-election-provider-support has finished. Result: https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756843 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/substrate/-/jobs/2756843/artifacts/download.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[gpestana]

Yes, we are still interested in merging this PR but are waiting for the opengov v1 to be completely deprecated and for the monorepo so that the merge is easier. Meanwhile, I will fix the conflicts.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[gpestana]

will work on this PR this week.