Add elastic scaling support in ParaInherent BenchBuilder

[sandreim]

Extracted Benchbuilder enhancements used in #3644 . Might still require some work to fully support all scenarios when disputing elastic scaling parachains, but it should be useful in writing elastic scaling runtime tests.

[alindima]

I suggest we also add the benchmark from #3644. The current code on master should already allow supplying multiple candidates if elastic scaling mvp feature is enabled (but only one will be backed). We have a test that does that:

polkadot-sdk/polkadot/runtime/parachains/src/inclusion/tests.rs

Line 1671 in d55d4f6

fn backing_works_with_elastic_scaling_mvp() {

[sandreim]

I suggest we also add the benchmark from #3644. The current code on master should already allow supplying multiple candidates if elastic scaling mvp feature is enabled (but only one will be backed). We have a test that does that:

polkadot-sdk/polkadot/runtime/parachains/src/inclusion/tests.rs

Line 1671 in d55d4f6

fn backing_works_with_elastic_scaling_mvp() {

Not sure which benchmark you are refering to. If you re talking about the big inherent, it just doesn't make sense, that is for testing purposes, we don't need that weight.

[alindima]

Not sure which benchmark you are refering to. If you re talking about the big inherent, it just doesn't make sense, that is for testing purposes, we don't need that weight.

A variation of the big inherent thingy. With realistic values, which exercises multiple candidates for a para (this is already allowed by the runtime). Otherwise, I'll add it in #3479 (but that PR is getting quite big and I could use the help :D )