[Feature]: Always derive aggregate keys from the signer set

[djordon]

Feature - Always derive aggregate keys the signer set

1. Description

Some places in the code base derive the aggregate key from the signer set, while other places just accept that the aggregate key matches the signer set. I believe we currently pass in the right thing, but better to make such a mistake impossible.

1.1 Context & Purpose

There are places in the code where it appears that we should do additional validation, but it would be best to ensure that this internal validation always happens so that there is no chance for programmer error.

2. Technical Details:

2.1 Acceptance Criteria:

• Make sure signer set is always mapped to the associated aggregate key.

3. Related Issues and Pull Requests (optional):

[djordon]

Oh, we cannot do this until #614 gets done.

[djordon]

Like in #614 (comment), I no longer think that we should do this.