Add missing metadata

[adamchainz]

Description

A quick check with Claude shows some missing new metadata:

Comparing the AWS docs with the package, here are the metadata categories available in AWS but not directly exposed by the ec2-metadata package:

1. ancestor-ami-ids
2. events/maintenance/history
3. events/maintenance/scheduled
4. metrics/vhostmd
5. network/interfaces/macs/{mac}/ipv6-prefix
6. placement/group-name
7. placement/host-id
8. placement/partition-number
9. product-codes
10. public-keys/0/openssh-key
11. spot/termination-time

Some dynamic data categories not directly exposed:

• fws/instance-monitoring
• instance-identity/pkcs7
• instance-identity/signature

We can add these on request.

[adamchainz]

public-keys/0/openssh-key done in #561