Allow `EventFilterBox::TriggerCompleted` as a trigger filter

[mversic]

          I still not sure why we should treat trigger completion event separately. 

It was requested like that in #2885, but reasons are not specified.

Originally posted by @Erigara in https://github.com/hyperledger/iroha/pull/4866#pullrequestreview-2191212630

[DCNick3]

I think the concern with allowing a trigger like that is that it can lead to infinite trigger loop if used improperly, possibly leading to DoS.

[Erigara]

Right now it not that hard to create such infinite loop as well.

You can create trigger which modifies it's own metadata and listen to events about metadata modifications of itself.

[mversic]

related #4429