JSON log encoder uses abbreviated field keys

[SurrealTiggi]

Description:
When using encoder: JSON in an EnvoyGateway logging config, the JSON output uses abbreviated field keys due to zap's encoder config, which can be cumbersome to deal with in a log aggregator:

Current example:

{"L":"INFO","T":"2026-03-16T10:49:01.641Z","N":"xds","C":"runner/runner.go:274","M":"received an update",...}

Aggregator friendlier format:

{"level":"info","ts":"2026-03-16T10:49:01.641Z","logger":"xds","caller":"runner/runner.go:274","msg":"received an update",...}

Would be great to have a means to either override the format (similar to other components), or provide a toggle or flag to use full field names.

[Relevant Links:]
This would be an extension of #6894 and #7455