Updates an existing ad hoc group, for a specified transaction, including any changes
to the group's members.

The request body structure is the same as creation:

• Array of member Role objects (existing or new members)
• The ad hoc group Role object with updated configuration

You can:

• Add new members by including their roles in the array
• Remove members by excluding them from the group.members array
• Update the group name via the signer's firstName
• Modify member types (AD_HOC_GROUP_MEMBER vs SIGNER)

Member types:

• AD_HOC_GROUP_MEMBER: Must sign if selected
• SIGNER: Optional member (can be selected to sign)