Uint64 field types

[urso]

Elasticsearch is adding support for uint64 types. Metrics based on system counters or IDs should make use of uint64 values.

Related issues/PRs:

• Elasticsearch: Introduce 64-bit unsigned long field type elasticsearch#60050, Add support for 64-bit unsigned integers elasticsearch#32434
• Beats: Reenable uint64 support beats#20188
• ECS: 64-bit unsigned integer field type usage  ecs#900