feat(resource): support list-valued resource attributes (PIPE-1253)

[Dylan-M]

Stacked on #278

Proposed Change

Lets a per-record resource attribute hold a list, which host identity needs for
host.ip and host.mac.

• Widens the resource attribute bag from map[string]string to map[string]any.
• The OTLP metrics builder serializes a []string resource value as an OTLP
  ArrayValue.

Only the OTLP metrics builder and stdout JSON serialize resource today; other
outputs drop it, unchanged.

Validation: run hostmetrics with the OTLP output and confirm a list-valued attribute
renders as an array in the payload. Tests assert a []string resource attribute
serializes to an OTLP array and scalars are unaffected.

Checklist

• Changes are tested
• CI has passed

[Dylan-M]

Warning

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• feat(config): reject invalid network CIDRs at environment load (PIPE-1002) #281
• feat(generators): emit simulated host identity on every record (PIPE-1036) #280
• feat(resource): support list-valued resource attributes (PIPE-1253) #279 👈 (View in Graphite)
• feat(datagen): environment foundations for simulated host identity (PIPE-1036) #278
• refactor(datagen): thread an injected logger, drop global-logger use (PIPE-1067) #277
• fix(datagen): return errors instead of panicking on developer-error input (PIPE-1003) #276
• feat(datagen): add IPv6 to NetworkIdentity and public emission (PIPE-1001) #275
• feat(datagen): add storage, network, and appliance-OS identities (PIPE-1035) #274
• main

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