feat: add proposer to MultisigExecutionInfo

[iamacook]

This adds MultisigExecutionInfo['proposer'] in accordance with safe-global/safe-client-gateway#1217.

[github-actions]

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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^{Report generated by eslint-plus-action}