Relaxing the `SendXcmOrigin` filter for some of the System chains:
- Relay Kusama: already open to signed origins and pluralities
- Relay Polkadot: relax to same level as Kusama ^

- Asset Hubs (P and K): open up to signed origins
- People (P and K): allow signed origins
- Encointer: allow signed origins

- Collectives Polkadot: no change, only Fellows collective allowed
- Bridge Hubs: no change, no arbitrary XCM sends allowed
- Coretime Kusama: no change, no arbitrary XCM sends allowed

We could allow it on all chains but on some of them there are no
usecases afaict, so starting out conservative, opening it up only
on chains where it's wanted.

…x-xcm-send-filter

…x-xcm-send-filter