Benchmark generic XCM instructions

[Agusrodri]

Adds benchmarking for XCM generic instructions of pallet_xcm_benchmarks::generic.

Also refactors benchmarks config inside the dancebox runtime. Individual calls to list_benchmark! and add_benchmark! macros were replaced by a single module called benches that contains all the desired pallets to be benchmarked in a cleaner way, making use of the define_benchmarks! macro.

[github-actions]

Master coverage: 74.51%
Coverage generated "Fri Sep 8 16:11:20 UTC 2023":
https://d3gkbsry1ehhqi.cloudfront.net/tanssi-coverage/pulls/248/index.html
Pull coverage: 71.92%

[girazoki]

LGTM. Note this is only generic instructions, so I would add that to the PR title. Do we envision how can we use them in templates as well?

[Agusrodri]

@girazoki if we need to implement these benchmarks for templates and Tanssi at the same time, we could build a common package and put the weights module inside it, but for it to be actually useful we should ensure that we want to use the same weights in templates and Tanssi all the time. Otherwise, if we start needing specific weights for each runtime, this module inside the common package will become useless.

So, is it planned that the templates and Tanssi use the same weights from now on? If that's the case, would you like me to apply the common package in this PR or in a separate one?

[girazoki]

lets for now keep it separate. We will evaluate later