likwidMetric.go: Add support for RAPL power limit

[ipatix]

To ease analysis of power limit vs actual power used.

[TomTheBear]

This requires a LIKWID library with sysfeatures enabled.

In the meantime, the rapl collector was enhanced to read the power limits from sysfs: 77fceb1

[ipatix]

TODO: Merge https://github.com/ClusterCockpit/cc-metric-collector/tree/rapl_collector_limits