Added support of `pallet-assets` and chain extension for it.

[xgreenx]

Added support of the chain extension for pallet-assets. The extension requires additional changes on the pallet-assets side to be ready for production. But we ca enable it already for testing=)

[HCastano]

I am a bit worried that this will make our update process more complicated because we are restrained to the substrate version your repo uses. But I see no better way here. We don't want a node per extension.

Maybe this is a good time for us to start pinning to release branches instead of following master. Green can do the same in the obce repo and we can more easily stay in lockstep there

[athei]

If you update your extension to use the polkadot-v0.9.29 branch we can merge this.