Migrate benchmarking imports from `frame_support::benchmarking` to `frame_benchmarking::v2`

[daniel-savu]

Is your feature request related to a problem? Please describe.
Imports from frame_support::benchmarking have been deprecated in polkadot-0.9.38, however this is not yet a breaking change.

Describe the solution you'd like
To avoid our benchmarks from breaking in the future, update imports and any syntax as described in the PR.

Describe alternatives you've considered
Could also wait until this becomes a breaking change.

[gregdhill]

This is mostly done, see #1043. We also did not yet update collator-selection to v2.