Feature/multisig setup build2

[mathewmeconry]

Description

Code4rena finding: code-423n4/2023-03-aragon-findings#86

• Adds prepareUpdate() to MultisigSetup
• Adds check that members length isn't > than uint16 during Multisig initialization
• Adds tests for Multisig update

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran all tests with success and extended them if necessary.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the test network.