Verify that all weight files were updated

[ggwpez]

Before a release happens and after all weight files were supposed to be updated, we should run a script to double-check the modification date of all weight files. Actually it would be better to check the //! DATE: comment, since the last git modification date could be unrelated to the re-generation of the weights.
The script that we currently use to run all benchmarks is not ideal; there are situations that pallets can go amiss.

We can limit he check to runtime weight files. It should be enough to filter for
"THIS FILE WAS AUTO-GENERATED USING THE SUBSTRATE BENCHMARK CLI" through all files, but good to double check with this file glob runtime/*/src/weights/**/*.rs,bridges/modules/*/src/weights.rs.
PS: //! DATE: ([0-9]+-[0-9]+-[0-9]+) looks like a good pattern.

(Not sure where to best put this issue so consider this as place holder)
cc @bkontur @coderobe

[s3krit]

Closing as #6996 is now merged