Support nested metadata matching

[rholshausen]

Being able to configure metadata matching at one or more levels deep and ignoring additional keys would also help us configure the metadata in contracts how we want to.

Ref: https://pact-foundation.slack.com/archives/C047TCR7B6W/p1686753876019769

[github-actions]

👋 Hi! The 'smartbear-supported' label has just been added to this issue, which will create an internal tracking ticket in PactFlow's Jira (PACT-1134). We will use this to prioritise and assign a team member to this task. All activity will be public on this ticket. For now, sit tight and we'll update this ticket once we have more information on the next steps.

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