Customise the trustedCall response mode

[Kailai-Wang]

Context

A follow-up issue of #1883
Now that we start to support both synchronous and asynchronous responses, we might want to discuss and decide which mode to use in practice.

There're a few options:

1. Try to detect it (e.g. by signer) and automatically select the mode
2. Always send both and it's up to the client which one to use => current implementation
3. Have a per-trustedCall configuration and follow it in the runtime, e.g.
   • set_user_shielding_key => DI response via ws
   • link_identity => II response via parachain
   • request-vc => both DI and II responses

cc @jonalvarezz @kaylawangnow

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[kziemianek]

The StfExecutor already knows which calls are submitted directly/indirectly so with this information we can conditionally send II/DI responses.

It means:

• for indirect invocations the node will send extrinsics back to parachain signaling processing result
• for direct invocations the node will send rpc responses back to client, but will not send extrinsics back to parachain
• if there is any state synchronization needed (for example after VC generation) it will be performed as it is

I can tackle it once #1957 is merged.

[Kailai-Wang]

for direct invocations the node will send rpc responses back to client, but will not send extrinsics back to parachain

Hold on about this one - for some request we might want both, or at least it will have both synchronous responses and parachain effects

[kziemianek]

@Kailai-Wang which case do you mean ? Isn't it covered by third dot (case vc_issued ) ?