Validate web API requests (#508)

* Adjust inbox worker pool capacity to default

* Adjust inbox worker pool capacity to default (#505)

* validate api requests

* release cachedInputs

Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>

* add payload size validation to sendPayload api

* Apply suggestions from code review

* validate transaction signatures

* refactor: move validation to packages

* update ValidateTransactionToAttach

* define errors

* Apply suggestions from code review

* fixes from codereview

Co-authored-by: jonastheis <mail@jonastheis.de>
Co-authored-by: Wolfgang Welz <welzwo@gmail.com>
Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>
Co-authored-by: Luca Moser <moser.luca@gmail.com>