feat(wallet): add external canister method call ui

[keplervital]

Adds the necessary missing components to surface the method call to an external canister, this also include the configuration of the approvals, policies, etc... for those external method calls.

At the moment the argument and reply constructions is not very helpful because we need to provide hex encoded argument and we get back a UInt8Array back as a response, as a follow up PR i'll give it a try to use candid parser to fetch the public metadata of the canister and have a better DX for that.

I'll mark the PR as ready once the following is completed:

• Test coverage

Views:

[olaszakos]

Enable external canister - List for admins by default?

[olaszakos]

Maybe add some info that the validation method must return with { Ok : text; Err : text }?