Describe the bug
_cache_key is getting generated incorrectly for mappings in ir.json, when using header with regex.

Steps to reproduce the behavior:
Create mapping with regex header (attached mapping.yaml)
Fetch ir.json generated by emissary (attached sample ir.json)
Check the _cache_key of the mappings inside the groups block.
Always _cache_key should be in the format of {kind}-{version}-{name}-{namespace}. But header_name is getting updated in the place of mapping name

Imapct
If we plan to use the _cache_key in any feature ticket, it could get impacted.

Expected behavior
Always _cache_key should be in defined format. {kind}-{version}-{name}-{namespace}

Versions (please complete the following information):

• Ambassador: 3.9.1
• Kubernetes environment: EKS
• Version: 1.28.9

Additional context
Attached the mapping.yaml and ir.json files.
incorrect-cache-key.zip