Benchmark for `deposit` in asset-index

[clearloop]

Issue summary

The benchmark of deposit in asset-index requires

• initial price pair in feat(asset-index): store initial price pair #106 (pallet_price_feed + pallet_chainlink_feed)
• Balances of caller ( pallet_asset_depository )

Something that blocks this issue is that we could not call pallet AssetDepository in the benchmark of AssetIndex directly by the limits of the benchmarking suitcase.

We'd better handle this after the unbounding things.

BTW, confused about having pallet_price_feed, pallet_asset_index, pallet_asset_depository, emmm, these pallets seems can be merged into one.

Other information and links

• Check if feed pair exists while adding asset in pallet asset index #94
• Complete pallet weights #230

[clearloop]

This should be an option of a checklist in #230